Consolidated Statements of Comprehensive Income Consolidated Statement of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Available-for-sale Securities, Tax	$ (130)	$ 1
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax	(38)	(24)
Other Comprehensive Income (Loss), Brokered Time Deposits, Tax	0	0
Other Comprehensive Income (Loss), Long Term Debt, Adjustment, Tax	1	(1)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax	$ 1	$ (1)