Shareholders' Equity - Adjustments to Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Class of Stock [Line Items]
Gains from sales of available-for-sale securities, net	$ 2	$ 0
Net interest income	664	673
Compensation and employee benefits expenses	1,208	1,229
Net income	634	508
Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Net income	5	(24)
Reclassification out of Accumulated Other Comprehensive Income | Net Unrealized Gains (Losses) on Available-for-Sale Securities
Class of Stock [Line Items]
Gains from sales of available-for-sale securities, net	1	0
Net realized gains from sales of available-for-sale securities, taxes	1	0
Reclassification out of Accumulated Other Comprehensive Income | Other-Than-Temporary Impairment on Securities
Class of Stock [Line Items]
Losses reclassified (from) to other comprehensive income	0	(1)
Other-than-temporary impairment on held-to-maturity securities related to factors other than credit, taxes	0	0
Reclassification out of Accumulated Other Comprehensive Income | Net Unrealized Gains (Losses) on Cash Flow Hedges
Class of Stock [Line Items]
Net interest income	(8)	(15)
Gain (loss) from cash flow hedge reclassified from accumulated other comprehensive income, taxes	(3)	(6)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Actuarial Losses
Class of Stock [Line Items]
Compensation and employee benefits expenses	12	(8)
Amortization of actuarial losses, taxes	$ 4	$ (4)