Loans - Additional Information (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other Real Estate	[1]	$ 62		$ 62		$ 99
Loans transferred from loans to loans held for sale		38	$ 362	1,734	$ 3,183
Transfer of Loans Held-for-sale to Portfolio Loans		75	19	726	39
Loans held for investment sold		178	2,300	1,994	2,954
Gain (Loss) on Sales of Loans, Net		9	$ 40	22	$ 71
Long-term Debt	[2]	8,444		8,444		13,022
Other Short-term Borrowings		1,077		1,077		5,634
Letters of Credit Outstanding, Amount		6,200		6,200		7,900
Loans held for investment	[3]	133,560		133,560		133,112
Accrual Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans in Process of Foreclosure, Amount	[4]	169		169		194
Financing Receivable, Modifications, Recorded Investment		$ 2,500		$ 2,500		$ 2,500
Accruing TDRs current		96.73%		96.73%		96.00%
Nonaccrual loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans in Process of Foreclosure, Amount	[4]	$ 99		$ 99		$ 152
Proceeds due from FHA or VA [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans in Process of Foreclosure, Amount	[4]	158		158		179
Other Real Estate	[4]	$ 50		$ 50		$ 57
Federal National Mortgage Association (FNMA) Insured Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Loan Portfolio Current		32.00%		32.00%		28.00%
Loans held for investment		$ 627		$ 627		$ 632
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Loan Portfolio Current		81.00%		81.00%		79.00%
Loans held for investment		$ 4,588		$ 4,588		$ 4,827
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		73,302		73,302		73,392
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		38,788		38,788		38,775
Home Equity Line of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[5]	13,416		13,416		14,264
Minimum [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Individually Evaluated For Impairment		3		3
Cross-Border Outstanding Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Foreign		$ 1,400		$ 1,400		$ 1,300
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan subcategory as a percent of total loans		29.00%		29.00%		29.00%
Government Guarantee Percent		2.00%		2.00%		2.00%
Home Equity Line of Credit [Member] | Credit Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unused Commitments to Extend Credit		$ 10,600		$ 10,600		$ 10,900
Mortgage Loans on Real Estate [Member] | Credit Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unused Commitments to Extend Credit		4,000		4,000		3,300
Federal Home Loan Bank Advances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other Short-term Borrowings						4,000
Federal Home Loan Bank Advances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term Debt		408		408		4,000
Federal Reserve Bank Advances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Pledged as Collateral		23,300		23,300		26,500
Line of Credit Facility, Remaining Borrowing Capacity		17,000		17,000		18,400
Federal Home Loan Bank Advances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Pledged as Collateral		32,000		32,000		31,200
Line of Credit Facility, Remaining Borrowing Capacity		26,200		26,200		24,300
Foreclosed [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other Real Estate	[1]	8		8		16
Foreclosed [Member] | Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other Real Estate	[1]	$ 50		$ 50		$ 75

[1] 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 funds are received and the property is conveyed. The receivable amount related to proceeds due from the FHA or the VA totaled $50 million and $57 million at September 30, 2015 and December 31, 2014, respectively.

[2] Includes debt of consolidated VIEs of $270 million and $302 million at September 30, 2015 and December 31, 2014, respectively.

[3] Includes loans of consolidated VIEs of $256 million and $288 million at September 30, 2015 and December 31, 2014, respectively.

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

[5] Excludes $627 million and $632 million of guaranteed residential loans at September 30, 2015 and December 31, 2014, respectively.