Shareholders' Equity - Adjustments to Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Class of Stock [Line Items]
Gains (losses) from sales of available-for-sale securities, net	$ 0		$ 9		$ 0	$ 8
Net interest income	613		659		1,286	1,302
Compensation and employee benefits expenses	1,084		1,125		2,313	2,374
Net income	587	$ 508	733	$ 659	1,095	1,392
Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Net income	4		12		(2)	28
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		7		0	6
Net realized gains from sales of available-for-sale securities, taxes	0		(2)		0	(3)
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)		(1)	(2)
Other-than-temporary impairment on held-to-maturity securities related to factors other than credit, taxes	0		0		0	0
Reclassification out of Accumulated Other Comprehensive Income | Net Unrealized Gains (Losses) on Cash Flow Hedges
Class of Stock [Line Items]
Net interest income	4		5		7	11
Gain (loss) from cash flow hedge reclassified from accumulated other comprehensive income, taxes	1		2		3	4
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Actuarial Losses
Class of Stock [Line Items]
Compensation and employee benefits expenses	0		1		(8)	13
Amortization of actuarial losses, taxes	$ 0		$ 1		$ (4)	$ 4