Accumulated Other Comprehensive Income (Components of Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other comprehensive income (loss) before tax
Net unrealized gain (loss)	$ 6,961	$ 430	$ (123)
Other reclassifications included in other revenue	(4)	(6)	0
Change in net unrealized gain (loss) on held to maturity securities:
Amortization of amounts previously recorded upon transfer to held to maturity from available for sale	0	36	35
Other	8	(14)	(1)
Other comprehensive income (loss), before tax	6,965	446	(89)
Tax effect
Net unrealized gain (loss)	(1,658)	(102)	30
Other reclassifications included in other revenue	1	1	0
Change in net unrealized gain (loss) on held to maturity securities:
Amortization of amounts previously recorded upon transfer from available for sale	0	(9)	(8)
Other	(2)	4	0
Other comprehensive income (loss)	(1,659)	(106)	22
Net of tax
Net unrealized gain (loss)	5,303	328	(93)
Other reclassifications included in other revenue	(3)	(5)	0
Change in net unrealized gain (loss) on held to maturity securities:
Amortization of amounts previously recorded upon transfer from available for sale	0	27	27
Other	6	(10)	(1)
Other comprehensive income (loss), net of tax	$ 5,306	$ 340	$ (67)