Shareholders' Equity - Adjustments to Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Class of Stock [Line Items]
Gains (losses) from sales of available-for-sale securities, net	$ 0	$ 2
Net interest income	467	664
Compensation and employee benefits expenses	1,242	1,208
Net income	519	634
Net realized gains from sales of available-for-sale securities, tax	0	1
Other comprehensive income (loss), cash flow hedge, gain (loss), reclassification, tax	6	2
Other comprehensive (income) loss, actuarial losses, tax	3	4
Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Net income	23	18
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	15	5
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Actuarial Losses
Class of Stock [Line Items]
Compensation and employee benefits expenses	$ 8	$ 12