Income Taxes - Net Deferred Tax Position (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Deferred tax assets:
Allowance for credit losses	$ 250		$ 267
Employee benefit accruals	142		120
Accrued expenses	110		334
Unused tax benefit carry-forwards	30		0
Bond premium amortization	226		143
Future federal tax benefit of state uncertain tax reserves	171		161
Interests in real estate mortgage investment conduits	309	[1]	188	[1]
Other	429		463
Total deferred tax assets	1,667		1,676
Less deferred tax liabilities:
Fair value adjustments	22		10
Unrealized gains (losses) on available-for-sale securities	(8)		692
Mortgage servicing rights	96		69
Total deferred tax liabilities	110		771
Net deferred tax asset	$ 1,557		$ 905

[1] Real estate mortgage investment conduits ("REMICs") are investment vehicles that hold commercial and residential mortgages in trust and issue securities representing an undivided interest in these mortgages.