Derivative Instruments - Additional Information (Detail) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Derivative Instrument Detail [Abstract]
Realized and unrealized gains (losses) on derivatives classified as cash flow hedges recorded in other comprehensive income (loss)	$ 52,000,000	$ 55,000,000
Non-derivative debt instruments designated as net investment hedges	1,200,000,000	$ 0
Fair value of derivatives under collateral agreements in a net liability position	685,000,000
Collateral posted by company netted against net liability position	663,000,000
Forward commitments to sell mortgage loans	5,800,000,000
Hedged mortgage loans held for sale	2,500,000,000
Unfunded mortgage loan commitments	$ 3,500,000,000