Other Borrowings (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2015	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt, Balance, Maturity and Termination [Line Items]
Other borrowings			$ 491	$ 4,971
Termination of legacy wholesale funding obligations	$ 4,400		4,400
Gains (Losses) on early extinguishment of debt	(39)	$ (73)	(112)	(71)	$ 0
Loss on Discontinuation of Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring	$ 370		370	0	$ 0
Trust Preferred Securities Subject to Mandatory Redemption [Member]
Debt, Balance, Maturity and Termination [Line Items]
Other borrowings			$ 409	428
Debt instrument maturity year			2031
Gains (Losses) on early extinguishment of debt			$ 4
Extinguishment of debt, amount			19
Repurchase Agreements [Member]
Debt, Balance, Maturity and Termination [Line Items]
Other borrowings			82	3,672
Securities Sold Under Agreements To Repurchase Maximum Month end Outstanding Amount			3,800	4,900
Federal Home Loan Bank Advances [Member]
Debt, Balance, Maturity and Termination [Line Items]
Other borrowings			0	920
Fair Value Hedge Adjustments And Deferred Costs [Member]
Debt, Balance, Maturity and Termination [Line Items]
Other borrowings			0	(49)
Total Securities Sold Under Agreements To Repurchase And FHLB Advances [Member]
Debt, Balance, Maturity and Termination [Line Items]
Other borrowings			82	4,543
Termination of legacy wholesale funding obligations			4,400
Loss on termination of wholesale funding obligations, pretax			413
Gains (Losses) on early extinguishment of debt			(43)
Loss on Discontinuation of Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring			370
Total Securities Sold Under Agreements to Repurchase and FHLB Advances and Trust Preferred Securities [Member]
Debt, Balance, Maturity and Termination [Line Items]
Other borrowings			$ 491	$ 4,971