Derivatives - Other Risk Management Derivatives (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest rate lock commitments
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives not designated as hedging	$ 220	$ 533	$ 714
Mortgage banking income \| Interest rate risk on mortgage banking income
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives not designated as hedging	8	461	254
Other income \| Credit risk on loans
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives not designated as hedging	(6)	(107)	(22)
Other income \| Interest rate and foreign currency risk on ALM activities
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives not designated as hedging	(36)	(754)	(222)
Personnel expense \| Price risk on restricted stock awards
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives not designated as hedging	$ 301	$ 9	$ (267)