Shareholders' Equity - Adjustments to Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Class of Stock [Line Items]
Gains (losses) from sales of available-for-sale securities, net	$ (1)			$ 0			$ (1)	$ 2
Net interest income	(487)			(478)			(1,421)	(1,701)
Compensation and employee benefits expenses	1,054			1,062			3,373	3,321
Net income	(714)	$ (763)	$ (519)	(555)	$ (694)	$ (634)	(1,996)	(1,883)
Other comprehensive income (loss), cash flow hedge, gain (loss), reclassification, tax	6			7			19	14
Net realized gains from sales of available-for-sale securities, tax							0	1
Other comprehensive (income) loss, actuarial losses, tax	1			1			5	5
Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Net income	(16)			(16)			(39)	(21)
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)			(17)			(51)	(37)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Actuarial Losses
Class of Stock [Line Items]
Compensation and employee benefits expenses	$ 2			$ 1			$ 12	$ 15