Accumulated Other Comprehensive Income (Loss) - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Tax (benefit) expense included in net unrealized gains (losses), investment securities	$ 13	$ (65)	$ 147	$ 243
Tax included in reclassification, investment securities	(2)	(6)	(11)	(30)
Tax included in amortization, investment securities	3	4	8	11
Cumulative effect of new accounting principle in period of adoption, tax					$ 103	$ 0
Tax (benefit) expense included in net unrealized gains (losses), fair value option liabilities	(26)	0	(78)	0
Tax (benefit) expense included in net unrealized gains (losses), cash flow hedges	(2)	5	(6)	(33)
Tax included in reclassification, cash flow hedges	$ 2	$ 2	$ 4	$ 5