Derivative Financial Instruments Derivative Instruments, Gain (Loss) (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Interest and Fee Income, Loans and Leases Held-in-portfolio		$ 1,549		$ 1,382		$ 4,424		$ 4,009
Interest Expense, Long-term Debt		(95)		(76)		(252)		(216)
Interest Expense, Deposits		(193)		(111)		(484)		(286)
Trading Gain (Loss)		42	[1]	51	[2]	137	[3]	148	[4]
Total Amounts of Line Items Presented in the Consolidated Statements of Income		1,303		1,246		3,825		3,655
Loans Held-For-Investment [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest and Fee Income, Loans and Leases Held-in-portfolio		1,549		1,382		4,424		4,009
Long-term Debt [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest Expense, Long-term Debt		(95)		(76)		(252)		(216)
Brokered Time Deposits [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest Expense, Long-term Debt		(193)
Interest Expense, Deposits				(111)		(484)		(286)
Other Trading [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Trading Gain (Loss)		42		51		137		148
Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Related to Interest Settlements on Derivatives		(2)		3		(1)		12
Derivative, Gain (Loss) on Derivative, Net		(33)		(3)		(130)		5
Gain (Loss) on Fair Value Hedges Recognized in Earnings		31		3		124		(4)
Net Income (Expense) Recognized on Hedges		(4)		3		(7)		13
Fair Value Hedging [Member] | Interest Rate Contract [Member] | Loans Held-For-Investment [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Related to Interest Settlements on Derivatives		0		0		0		0
Derivative, Gain (Loss) on Derivative, Net		0		0		0		0
Gain (Loss) on Fair Value Hedges Recognized in Earnings		0		0		0		0
Net Income (Expense) Recognized on Hedges		0		0		0		0
Fair Value Hedging [Member] | Interest Rate Contract [Member] | Long-term Debt [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Related to Interest Settlements on Derivatives		(2)		3		(1)		12
Derivative, Gain (Loss) on Derivative, Net		(33)		0		(130)		0
Gain (Loss) on Fair Value Hedges Recognized in Earnings		31	[5]	0		124	[5]	0
Net Income (Expense) Recognized on Hedges		(4)		3		(7)		12
Fair Value Hedging [Member] | Interest Rate Contract [Member] | Brokered Time Deposits [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Related to Interest Settlements on Derivatives		0		0		0		0
Derivative, Gain (Loss) on Derivative, Net		0		0		0		0
Gain (Loss) on Fair Value Hedges Recognized in Earnings		0		0		0		0
Net Income (Expense) Recognized on Hedges		0		0		0		0
Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other Trading [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Related to Interest Settlements on Derivatives		0		0		0		0
Derivative, Gain (Loss) on Derivative, Net		0		(3)		0		5
Gain (Loss) on Fair Value Hedges Recognized in Earnings		0		3		0		(4)
Net Income (Expense) Recognized on Hedges		0		0		0		1
Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		(22)		13		(39)		81
Net Income (Expense) Recognized on Hedges		(22)		13		(39)		81
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Loans Held-For-Investment [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	[6]	(22)		13		(39)		81
Net Income (Expense) Recognized on Hedges		(22)		13		(39)		81
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Long-term Debt [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		0		0		0		0
Net Income (Expense) Recognized on Hedges		0		0		0		0
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Brokered Time Deposits [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		0		0		0		0
Net Income (Expense) Recognized on Hedges		0		0		0		0
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Other Trading [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		0		0		0		0
Net Income (Expense) Recognized on Hedges		0		0		0		0
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		9		53		5		143
Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Mortgage Servicing Rights [Member] | Mortgage Servicing Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		(54)		17		(210)		41
Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Loans Held-For-Sale [Member] | Mortgage Production Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		10		(20)		57		(57)
Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Loans Held-For-Investment [Member] | Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		1		0		3		(1)
Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other Trading [Member] | Other Trading [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		18		11		48		33
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Trading [Member] | Other Trading [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		9		(10)		49		(43)
Not Designated as Hedging Instrument [Member] | Credit Risk Contract [Member] | Loans Held-For-Investment [Member] | Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		(5)		(1)		(5)		(3)
Not Designated as Hedging Instrument [Member] | Credit Risk Contract [Member] | Other Trading [Member] | Other Trading [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		5		8		16		19
Not Designated as Hedging Instrument [Member] | Equity Contract [Member] | Other Trading [Member] | Other Trading [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		6		(1)		8		(1)
Not Designated as Hedging Instrument [Member] | Other Contract [Member] | Interest Rate Lock Commitments [Member] | Mortgage Production and Commercial Real Estate Related Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		19		49		39		154
Not Designated as Hedging Instrument [Member] | Other Contract [Member] | Commodity Contract [Member] | Other Trading [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		$ 0		$ 0		$ 0		$ 1

[1] Amounts are presented in accordance with ASC Topic 606, Revenue from Contracts with Customers, except for out of scope amounts.

[2] Amounts for periods prior to January 1, 2018 are presented in accordance with ASC Topic 605, Revenue Recognition, and have not been restated to conform with ASC Topic 606, Revenue from Contracts with Customers.

[3] Amounts are presented in accordance with ASC Topic 606, Revenue from Contracts with Customers, except for out of scope amounts.

[4] Amounts for periods prior to January 1, 2018 are presented in accordance with ASC Topic 605, Revenue Recognition, and have not been restated to conform with ASC Topic 606, Revenue from Contracts with Customers.

[5] Includes amortization from de-designated fair value hedging relationships.

[6] These amounts include pre-tax gains/(losses) related to cash flow hedging relationships that have been terminated and were reclassified into earnings consistent with the pattern of net cash flows expected to be recognized.