Shareholders' Equity - Adjustments to Accumulated Other Comprehensive Income (Details) - USD ($)	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Class of Stock [Line Items]
Gains (losses) from sales of available-for-sale securities, net	$ 0			$ 0			$ 0	$ 8,000,000
Net interest income	644,000,000			672,000,000			1,930,000,000	1,974,000,000
Compensation and employee benefits expenses	1,083,000,000			1,103,000,000			3,396,000,000	3,477,000,000
Net income	583,000,000	$ 587,000,000	$ 508,000,000	764,000,000	$ 733,000,000	$ 659,000,000	1,678,000,000	2,156,000,000
Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Net income	2,000,000			4,000,000			0	32,000,000
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			0			0	6,000,000
Net realized gains from sales of available-for-sale securities, taxes	0			0			0	(2,000,000)
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)			(1,000,000)	(3,000,000)
Other-than-temporary impairment on held-to-maturity securities related to factors other than credit, taxes	0			0			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	3,000,000			4,000,000			10,000,000	15,000,000
Gain (loss) from cash flow hedge reclassified from accumulated other comprehensive income, taxes	1,000,000			2,000,000			4,000,000	6,000,000
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			(9,000,000)	14,000,000
Amortization of actuarial losses, taxes	$ (1,000,000)			$ 1,000,000			$ (5,000,000)	$ 5,000,000