Securities Available for Sale and Securities Held to Maturity (Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Securities Available for Sale) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale Amortized Cost	$ 52,908		$ 51,604
Securities available for sale Gross Unrealized Gains	338		255
Securities available for sale Gross Unrealized Losses	166		241
Securities available for sale	53,080		51,618
U.S. agency mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale Amortized Cost	18,404		18,554
Securities available for sale Gross Unrealized Gains	168		140
Securities available for sale Gross Unrealized Losses	38		49
Securities available for sale	18,534	[1]	18,645
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale Amortized Cost	16,642		15,201
Securities available for sale Gross Unrealized Gains	91		42
Securities available for sale Gross Unrealized Losses	8		37
Securities available for sale	16,725		15,206
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale Amortized Cost	9,043		8,973
Securities available for sale Gross Unrealized Gains	53		49
Securities available for sale Gross Unrealized Losses	9		15
Securities available for sale	9,087		9,007
U.S. agency notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale Amortized Cost	4,490		4,239
Securities available for sale Gross Unrealized Gains	1		1
Securities available for sale Gross Unrealized Losses	81		104
Securities available for sale	4,410		4,136
Certificates of deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale Amortized Cost	3,424		3,650
Securities available for sale Gross Unrealized Gains	4		4
Securities available for sale Gross Unrealized Losses	2		2
Securities available for sale	3,426		3,652
Non-agency residential mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale Amortized Cost	593		616
Securities available for sale Gross Unrealized Gains	13		11
Securities available for sale Gross Unrealized Losses	28		34
Securities available for sale	578	[1]	593
Non-agency commercial mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale Amortized Cost	312		271
Securities available for sale Gross Unrealized Gains	8		8
Securities available for sale	320	[1]	279
Other securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale Amortized Cost			100
Securities available for sale			$ 100

[1] Mortgage-backed securities have been allocated to maturity groupings based on final contractual maturities. Actual maturities will differ from final contractual maturities because borrowers on a certain portion of loans underlying these securities have the right to prepay their obligations.