Income Taxes - Continuing Operations (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Provision (benefit) for income taxes		$ 907	$ 61	$ 108	$ 152	$ (11)	$ 26	$ (5)	$ 79	$ 1,228	$ 89	$ 230
Income tax expense (benefit) included in common equity related to:
Unrealized gains (losses) on investment securities										127	(135)	(242)
Unrealized gains (losses) on fair value option liabilities attributable to our own credit spread(1)	[1]									(115)	0	0
Unrealized gains (losses) on derivatives designated as cash flow hedges										(5)	9	2
Employer accounting for post-retirement plans										1	2	0
Total income taxes										$ 1,236	$ (35)	$ (10)

[1] See Note 2, "Summary of Significant Accounting Policies and New Accounting Pronouncements," for information on the adoption of new accounting guidance on January 1, 2017 related to fair value option liabilities attributable to our own credit spread.