Shareholders' Equity - Adjustments to Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Class of Stock [Line Items]
Gains (losses) from sales of available-for-sale securities, net	$ 0		$ 0		$ 0	$ 2
Net interest income	467		559		934	1,223
Compensation and employee benefits expenses	1,077		1,051		2,319	2,259
Net income	763	$ 519	694	$ 634	1,282	1,328
Other comprehensive income (loss), cash flow hedge, gain (loss), reclassification, tax	7		6		13	8
Net realized gains from sales of available-for-sale securities, tax					0	1
Other comprehensive (income) loss, actuarial losses, tax	1		0		4	4
Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Net income	20		17		43	35
Reclassification out of Accumulated Other Comprehensive Income | Net Unrealized Gains (Losses) on Available-for-Sale Securities
Class of Stock [Line Items]
Gains (losses) from sales of available-for-sale securities, net					0	1
Reclassification out of Accumulated Other Comprehensive Income | Net Unrealized Gains (Losses) on Cash Flow Hedges
Class of Stock [Line Items]
Net interest income	18		15		33	20
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Actuarial Losses
Class of Stock [Line Items]
Compensation and employee benefits expenses	$ 2		$ 2		$ 10	$ 14