Shareholders' Equity - Adjustments to Accumulated Other Comprehensive Income (Details) - USD ($)	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Class of Stock [Line Items]
Gains from sales of available-for-sale securities, net	$ 0			$ 0			$ 2,000,000	$ 0
Net interest income	478,000,000			644,000,000			1,701,000,000	1,930,000,000
Compensation and employee benefits expenses	1,062,000,000			1,083,000,000			3,321,000,000	3,396,000,000
Net income	555,000,000	$ 694,000,000	$ 634,000,000	583,000,000	$ 587,000,000	$ 508,000,000	1,883,000,000	1,678,000,000
Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Net income	18,000,000			2,000,000			53,000,000	0
Reclassification out of Accumulated Other Comprehensive Income | AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent
Class of Stock [Line Items]
Gains from sales of available-for-sale securities, net	0			0			1,000,000	0
Net realized gains from sales of available-for-sale securities, taxes	0			0			1,000,000	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	(1,000,000)
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 | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Class of Stock [Line Items]
Net interest income	17,000,000			3,000,000			37,000,000	10,000,000
Gain (loss) from cash flow hedge reclassified from accumulated other comprehensive income, taxes	7,000,000			1,000,000			14,000,000	4,000,000
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Actuarial Losses
Class of Stock [Line Items]
Compensation and employee benefits expenses	1,000,000			(1,000,000)			15,000,000	(9,000,000)
Amortization of actuarial losses, taxes	$ 1,000,000			$ (1,000,000)			$ 5,000,000	$ (5,000,000)