Derivative Financial Instruments Derivative Instruments, Gain (Loss) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Interest and fees on loans		$ 1,398	$ 1,289
Interest Expense, Long-term Debt		(74)	(70)
Interest on deposits		(131)	(80)
Total Amounts of Line Items Presented in the Consolidated Statements of Income		1,193
Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Related to Interest Settlements on Derivatives		3
Derivative, Gain (Loss) on Derivative, Net		(72)
Gain (Loss) on Fair Value Hedges Recognized in Earnings		69
Net Income (Expense) Recognized on Hedges		0
Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other Trading [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net			(11)
Gain (Loss) on Fair Value Hedges Recognized in Earnings			13
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net			2
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		3
Derivative, Gain (Loss) on Derivative, Net		(72)
Gain (Loss) on Fair Value Hedges Recognized in Earnings	[1]	69
Net Income (Expense) Recognized on Hedges		0
Fair Value Hedging [Member] | Interest Rate Contract [Member] | Long-term Debt [Member] | Other Trading [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net	[2]		(11)
Gain (Loss) on Fair Value Hedges Recognized in Earnings	[2]		13
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net	[2]		2
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
Derivative, Gain (Loss) on Derivative, Net		0
Gain (Loss) on Fair Value Hedges Recognized in Earnings		0
Net Income (Expense) Recognized on Hedges		0
Fair Value Hedging [Member] | Interest Rate Contract [Member] | Brokered Time Deposits [Member] | Other Trading [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net	[2]		0
Gain (Loss) on Fair Value Hedges Recognized in Earnings	[2]		0
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net	[2]		0
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
Derivative, Gain (Loss) on Derivative, Net		0
Gain (Loss) on Fair Value Hedges Recognized in Earnings		0
Net Income (Expense) Recognized on Hedges		0
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			(5)
Net Income (Expense) Recognized on Hedges		(5)
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
Net Income (Expense) Recognized on Hedges		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
Net Income (Expense) Recognized on Hedges		0
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	[3]		(5)
Net Income (Expense) Recognized on Hedges		(5)
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Loans Held-For-Investment [Member] | Interest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	[4]		23
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	[4]	$ (165)	$ (25)

[1] Includes $2 million of amortization expense from de-designated fair value hedging relationships.

[2] Amounts are recognized in Trading income in the Consolidated Statements of Income.

[3] During the three months ended March 31, 2018, the Company also reclassified $4 million of pre-tax gains from AOCI into Net interest income relating to hedging relationships that have been terminated and are reclassified into earnings consistent with the pattern of net cash flows expected to be recognized.

[4] During the three months ended March 31, 2017, the Company also reclassified $18 million of pre-tax gains from AOCI into Net interest income relating to hedging relationships that have been terminated and are reclassified into earnings consistent with the pattern of net cash flows expected to be recognized.