Shareholders' Equity - Adjustments to Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Class of Stock [Line Items]
Gains (losses) from sales of available-for-sale securities, net	$ 0	$ (1)
Compensation and employee benefits expenses	1,229	1,249
Net income	508	659
Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Net income	(9)	10
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)
Net realized gains from sales of available-for-sale securities, taxes	0	(1)
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	(1)	(1)
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 | Amortization of Actuarial Losses
Class of Stock [Line Items]
Compensation and employee benefits expenses	(8)	12
Amortization of actuarial losses, taxes	$ (4)	$ 3