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	Jun. 30, 2013	Dec. 31, 2012
HTM securities, amortized cost	$ 13,751	$ 13,594
HTM securities, gross unrealized gains	34	260
HTM securities, gross unrealized losses	340	6
HTM securities, fair value	13,445	13,848
GSE Securities
HTM securities, amortized cost	5,200	3,808
HTM securities, gross unrealized gains	0	17
HTM securities, gross unrealized losses	272	1
HTM securities, fair value	4,928	3,824
RMBS Issued by GSE
HTM securities, amortized cost	8,059	9,273
HTM securities, gross unrealized gains	27	238
HTM securities, gross unrealized losses	68	1
HTM securities, fair value	8,018	9,510
States and Political Subdivisions [Member]
HTM securities, amortized cost	33	34
HTM securities, gross unrealized gains	1	1
HTM securities, gross unrealized losses	0	1
HTM securities, fair value	34	34
Other Securities [Member]
HTM securities, amortized cost	459	479
HTM securities, gross unrealized gains	6	4
HTM securities, gross unrealized losses	0	3
HTM securities, fair value	$ 465	$ 480