Fair Value Disclosures - Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Commitments to extend, originate or purchase credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/ Contract Amount	$ 64,174	$ 59,019
Fair Value	265	253
Residential mortgage loans sold with recourse
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/ Contract Amount	610	702
Fair Value	8	8
Other loans sold with recourse
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/ Contract Amount	4,053	4,198
Fair Value	7	7
Letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/ Contract Amount	2,952	3,033
Fair Value	$ 29	$ 27