With the persona of a small bank - albeit one sitting within a very large wealth management and diversified financial services operation - AMP Bank has, with its double digit performance, provided the understated highlight of the past year for AMP Group.AMP Bank's underlying profit hit A$1.04 billion, an increase of 114 per cent.Its operating earnings rose 17 per cent to $140 million (in comparison, the bank's earnings in the 2016 year were $120 million). The strong performance was largely due to a 14 per cent rise in residential lending to $18.9 billion, underpinned by a conservative credit policy, AMP said in a media statement.This was despite a moderation in the second half of the 2017 year, as the market adjusted to new regulatory requirements for residential lending.Controllable costs increased in FY 2017, reflecting investment in people and technology to support growth. The cost to income ratio, however, remained almost flat at 28.6 per cent - in fact the year-on-year difference was more likely due to a rounding error (the FY 2016 cost to income ratio was 28.5 per cent).In further management commentary, AMP noted it has "maintained conservative credit policy and asset quality [has] remained strong; 90-plus day arrears well below industry average." The capital position strengthened "in response to response to changing regulatory requirements and to support continuing loan growth", the bank said.Other key metrics:•    Net interest margin for FY 2017: 1.70 per cent (up from 1.67 per cent in FY 2016)•    Residential mortgage book:   $18.9 billion (up from $16.5 billion)•    Deposits (A$m):    Almost $12.4 billion (up from $11.5 billion) •    Return on capital:  16.5 per cent (up from 16.7 per cent)•    Liquidity coverage ratio:  126 per cent (up from 144 per cent)