Shareholders' Equity - Adjustments to Accumulated Other Comprehensive Income (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Net interest income	$ 2,200,000,000	$ 2,566,000,000	$ 2,671,000,000
Compensation and employee benefits expenses	4,450,000,000	4,541,000,000	4,780,000,000
Net income	2,420,000,000	2,242,000,000	$ 2,593,000,000
Other-than-temporary impairment on held-to-maturity securities related to factors other than credit, taxes	0	0
Gain (loss) from cash flow hedge reclassified from accumulated other comprehensive income, taxes	20,000,000	5,000,000
Amortization of actuarial losses, taxes	3,000,000	(8,000,000)
Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Net income	61,000,000	(5,000,000)
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)
Reclassification out of Accumulated Other Comprehensive Income | Net Unrealized Gains (Losses) on Cash Flow Hedges
Class of Stock [Line Items]
Net interest income	52,000,000	12,000,000
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Actuarial Losses
Class of Stock [Line Items]
Compensation and employee benefits expenses	$ 9,000,000	$ (16,000,000)