Other Assets - Additional Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Other Assets [Abstract]
Amortization method qualified affordable housing projects investments	$ 828	$ 853
Qualified affordable housing project investments, commitment	339	358
Qualified affordable housing project commitment - 2015	135
Qualified affordable housing project commitment - 2016	110
Qualified affordable housing project commitment - 2017	82
Qualified affordable housing project commitment - 2018	2
Qualified affordable housing project commitment - 2019	1
Qualified affordable housing project commitment - 2020 and thereafter	9
Affordable housing tax credits and other tax benefits, amount	33	34	31
Qualified affordable housing project investments, amortization	$ 24	$ 26	$ 24