Commitments and Contingencies - Summary (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Letters of credit	$ 3,004	$ 3,033
Carrying amount of the liability for letters of credit	30	27
Investments in affordable housing and historic building rehabilitation projects:
Carrying amount	1,767	1,629
Amount of future funding commitments included in carrying amount	790	654
Lending exposure	315	292
Tax credits subject to recapture	355	355
Private equity and similar investments	301	289
Future funding commitments to consolidated private equity funds	$ 224	$ 231