Loans - Additional Information (Details) - USD ($)		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transfer of Portfolio Loans and Leases to Held-for-sale		$ 55,000,000	$ 512,000,000
Transfer of Loans Held-for-sale to Portfolio Loans		5,000,000	11,000,000
Loans held for investment sold		$ 18,000,000	405,000,000
Gain (Loss) on Sales of Loans, Net			$ 6,000,000
Document Period End Date		Mar. 31, 2016
Long-term Debt	[1]	$ 8,514,000,000		$ 8,462,000,000
Other Short-term Borrowings		1,673,000,000		1,024,000,000
Letters of Credit Outstanding, Amount		7,200,000,000		6,700,000,000
Other Real Estate	[2]	52,000,000		56,000,000
Loans and Leases Receivable, Impaired, Commitment to Lend		1,000,000		4,000,000
Loans held for investment	[3]	$ 139,746,000,000		136,442,000,000
Government Guarantee Percent		2.00%
Accrual Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Recorded Investment		$ 2,500,000,000		$ 2,600,000,000
Percentage Of Accruing Troubled Debt Restructurings, Current		97.00%		97.00%
Mortgage Loans in Process of Foreclosure, Amount	[4]	$ 155,000,000		$ 152,000,000
Nonaccrual loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans in Process of Foreclosure, Amount	[4]	123,000,000		112,000,000
Proceeds due from FHA or VA [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans in Process of Foreclosure, Amount	[4]	144,000,000		141,000,000
Other Real Estate	[4]	$ 48,000,000		$ 52,000,000
Federal National Mortgage Association (FNMA) Insured Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Loan Portfolio Current		32.00%		31.00%
Loans held for investment		$ 623,000,000		$ 629,000,000
Government Guarantee Percent				0.00%
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Loan Portfolio Current		79.00%		78.00%
Loans held for investment		$ 5,265,000,000		$ 4,922,000,000
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other Real Estate	[2]	9,000,000		11,000,000
Loans held for investment		77,495,000,000		75,252,000,000
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other Real Estate	[2]	39,000,000		39,000,000
Loans held for investment		38,999,000,000		38,928,000,000
Mortgage Loans on Real Estate		0.28		0.29
Home Equity Line of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[5]	12,845,000,000		13,171,000,000
Minimum [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Individually Evaluated For Impairment		3,000,000
Cross-Border Outstanding Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Foreign		2,000,000,000		1,600,000,000
Home Equity Line of Credit [Member] | Credit Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unused Commitments to Extend Credit		10,600,000,000		10,500,000,000
Mortgage Loans on Real Estate [Member] | Credit Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unused Commitments to Extend Credit		3,600,000,000		3,200,000,000
Federal Home Loan Bank Advances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term Debt		408,000,000		400,000,000
Other Short-term Borrowings		750,000,000
Federal Reserve Bank Advances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Pledged as Collateral		23,900,000,000		23,600,000,000
Line of Credit Facility, Remaining Borrowing Capacity		16,800,000,000		17,200,000,000
Federal Home Loan Bank Advances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Pledged as Collateral		34,200,000,000		33,700,000,000
Line of Credit Facility, Remaining Borrowing Capacity		$ 28,900,000,000		$ 28,500,000,000

[1] Includes debt of consolidated VIEs of $250 million and $259 million at March 31, 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 $48 million and $52 million at March 31, 2016 and December 31, 2015, respectively.

[3] Includes loans of consolidated VIEs of $237 million and $246 million at March 31, 2016 and December 31, 2015, respectively.

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

[5] Excludes $623 million and $629 million of guaranteed residential loans at March 31, 2016 and December 31, 2015, respectively.