Loans - Additional Information (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transfer of Portfolio Loans and Leases to Held-for-sale		$ 107	$ 1,200	$ 162	$ 1,700
Transfer of Loans Held-for-sale to Portfolio Loans		5	640	10	651
Loans held for investment sold		260	1,400	278	1,800
Gain (Loss) on Sales of Loans, Net		(2)	$ 7	(2)	$ 13
Long-term Debt	[1]	12,264		12,264		$ 8,462
Other Short-term Borrowings		1,883		1,883		1,024
Letters of Credit Outstanding, Amount		3,200		3,200		6,700
Other Real Estate	[2]	49		49		56
Loans and Leases Receivable, Impaired, Commitment to Lend		1		1		4
Loans held for investment	[3]	141,656		141,656		136,442
Accrual Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Recorded Investment		$ 2,500		$ 2,500		$ 2,600
Percentage Of Accruing Troubled Debt Restructurings, Current		97.00%		97.00%		97.00%
Mortgage Loans in Process of Foreclosure, Amount	[4]	$ 138		$ 138		$ 152
Nonaccrual loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans in Process of Foreclosure, Amount	[4]	127		127		112
Proceeds due from FHA or VA [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans in Process of Foreclosure, Amount	[4]	128		128		141
Other Real Estate		$ 52		$ 52		$ 52	[4]
Federal National Mortgage Association (FNMA) Insured Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Loan Portfolio Current		29.00%		29.00%		31.00%
Loans held for investment		$ 534		$ 534		$ 629
Government Guarantee Percent		1.00%		1.00%		2.00%
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Loan Portfolio Current		80.00%		80.00%		78.00%
Loans held for investment		$ 5,562		$ 5,562		$ 4,922
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other Real Estate	[2]	9		9		11
Loans held for investment		77,448		77,448		75,252
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other Real Estate	[2]	37		37		39
Loans held for investment		$ 39,449		$ 39,449		$ 38,928
Percentage of Loans Held for Investment		28.00%		28.00%		29.00%
Home Equity Line of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[5]	$ 12,481		$ 12,481		$ 13,171
Geographic Distribution, Foreign [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		1,700		1,700		1,600
Minimum [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Individually Evaluated For Impairment		3		3		3
Home Equity Line of Credit [Member] | Credit Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unused Commitments to Extend Credit		10,500		10,500		10,500
Mortgage Loans on Real Estate [Member] | Credit Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unused Commitments to Extend Credit		7,000		7,000		3,200
Federal Home Loan Bank Advances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term Debt		3,400		3,400		408
Other Short-term Borrowings		1,000		1,000
Federal Reserve Bank Advances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Pledged as Collateral		24,500		24,500		23,600
Line of Credit Facility, Remaining Borrowing Capacity		17,600		17,600		17,200
Federal Home Loan Bank Advances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Pledged as Collateral		35,000		35,000		33,700
Line of Credit Facility, Remaining Borrowing Capacity		$ 29,900		$ 29,900		$ 28,500

[1] Includes debt of consolidated VIEs of $240 million and $259 million at June 30, 2016 and December 31, 2015, respectively.

[2] Does not include foreclosed real estate related to loans insured by the FHA or the VA. Proceeds due from the FHA and the VA are recorded as a receivable in other assets in the Consolidated Balance Sheets until the property is conveyed and the funds are received. The receivable related to proceeds due from the FHA or the VA totaled $52 million at both June 30, 2016 and December 31, 2015.

[3] Includes loans of consolidated VIEs of $227 million and $246 million at June 30, 2016 and December 31, 2015, respectively.

[4] Nonaccruing restructured loans are included in total nonaccrual/NPLs.

[5] Excludes $534 million and $629 million of guaranteed residential loans at June 30, 2016 and December 31, 2015, respectively.