Commitments and Contingencies - Summary (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Letters of credit	$ 2,952	$ 3,033
Carrying amount of the liability for letters of credit	29	27
Investments in affordable housing and historic building rehabilitation projects:
Carrying amount	1,738	1,629
Amount of future funding commitments included in carrying amount	774	654
Lending exposure	549	292
Tax credits subject to recapture	393	355
Private equity and similar investments	340	289
Future funding commitments to consolidated private equity funds	$ 210	$ 231