Standard & Poor's has raised AMP Bank's stand-alone credit profile despite keeping the ratings of its parent AMP Ltd on negative credit watch.In a report issued on Tuesday, the ratings agency revealed it had revised the bank's credit profile to "bbb" from "bbb-".S&P has also placed AMP's banking arm on a stable outlook because it expects the business to maintain a risk-adjusted capital ratio above 15 per cent over the next 18 months.While uncertainty surrounds the financial impact on the AMP group of litigation and regulatory sanctions flowing from the "fees for no service" scandal, S&P indicated that the bank would be shielded from a ratings downgrade of the parent and its holding company.AMP Bank's capital position was boosted towards the end of last year after the parent contributed an additional $30 million of common equity in the business."The increased capital will offset the potential for a downgrade of the bank in the event of a one-notch downgrade of AMP Group Holdings Limited," S&P said.The S&P action is significant for the banking arm as it should give managing director Sally Bruce and her management team greater certainty around the near-term funding costs of the company."We believe downward rating prospects are reasonably limited for the bank over the next two years," the agency observed.AMP Bank grew operating earnings by 17 per cent to A$140 million last year on the back of solid home lending growth and an industry-leading cost-to-income ratio of 28.6 per cent.The ratings agency expects the bank's contribution to group profit to rise from the current level of 15 per cent."AMP Bank's earnings contribution to the group should increase, based on the targeted growth of the banking operations and efforts to better embed products within the wider group offerings," S&P said."With that aim, the bank's use of AMP-aligned advisers for mortgage originations should grow."However, the ratings agency believes the bank will continue to rely on mortgage brokers to originate most of its lending business.