Securities (Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Approximate Fair Values of Securities Held to Maturity) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
HTM securities, amortized cost	$ 18,101	$ 13,594
HTM securities, gross unrealized gains	54	260
HTM securities, gross unrealized losses	625	6
HTM securities, fair value	17,530	13,848
U.S. Treasury Securities
HTM securities, amortized cost	392
HTM securities, gross unrealized gains	0
HTM securities, gross unrealized losses	8
HTM securities, fair value	384
GSE Securities
HTM securities, amortized cost	5,603	3,808
HTM securities, gross unrealized gains	2	17
HTM securities, gross unrealized losses	397	1
HTM securities, fair value	5,208	3,824
MBS Issued by GSE
HTM securities, amortized cost	11,636	9,273
HTM securities, gross unrealized gains	38	238
HTM securities, gross unrealized losses	220	1
HTM securities, fair value	11,454	9,510
States and Political Subdivisions [Member]
HTM securities, amortized cost	33	34
HTM securities, gross unrealized gains	2	1
HTM securities, gross unrealized losses	0	1
HTM securities, fair value	35	34
Other Securities [Member]
HTM securities, amortized cost	437	479
HTM securities, gross unrealized gains	12	4
HTM securities, gross unrealized losses	0	3
HTM securities, fair value	$ 449	$ 480