Derivative Financial Instruments Derivative Instruments, Gain (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Interest and Fee Income, Loans and Leases Held-in-portfolio		$ 6,058		$ 5,385	$ 4,939
Interest Expense, Long-term Debt		(375)		(288)	(260)
Interest Expense, Deposits		(711)		(404)	(259)
Trading Gain (Loss)		161		189	211
Total Amounts of Line Items Presented in the Consolidated Statements of Income		5,133		4,882	4,631
Loans Held-For-Investment [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest and Fee Income, Loans and Leases Held-in-portfolio		6,058		5,385	4,939
Long-term Debt [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest Expense, Long-term Debt		(375)		(288)	(260)
Brokered Time Deposits [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest Expense, Deposits		(711)		(404)	(259)
Other Trading [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Trading Gain (Loss)		161		189	211
Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Related to Interest Settlements on Derivatives		(1)		15	17
Derivative, Gain (Loss) on Derivative, Net		(24)		(38)	(87)
Gain (Loss) on Fair Value Hedges Recognized in Earnings		11		40	89
Net Income (Expense) Recognized on Hedges		(14)		17	19
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
Derivative, Gain (Loss) on Derivative, Net		0		0	0
Gain (Loss) on Fair Value Hedges Recognized in Earnings		0		0	0
Net Income (Expense) Recognized on Hedges		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		(1)		15	17
Derivative, Gain (Loss) on Derivative, Net		(24)		0	0
Gain (Loss) on Fair Value Hedges Recognized in Earnings		11	[1]	0	0
Net Income (Expense) Recognized on Hedges		(14)		15	17
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
Derivative, Gain (Loss) on Derivative, Net		0		0	0
Gain (Loss) on Fair Value Hedges Recognized in Earnings		0		0	0
Net Income (Expense) Recognized on Hedges		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
Derivative, Gain (Loss) on Derivative, Net		0		(38)	(87)
Gain (Loss) on Fair Value Hedges Recognized in Earnings		0		40	89
Net Income (Expense) Recognized on Hedges		0		2	2
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		(72)		89	244
Net Income (Expense) Recognized on Hedges		(72)		89	244
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	[2]	(72)		89	244
Net Income (Expense) Recognized on Hedges		(72)		89	244
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
Net Income (Expense) Recognized on Hedges		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
Net Income (Expense) Recognized on Hedges		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
Net Income (Expense) Recognized on Hedges		$ 0		$ 0	$ 0

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

[2] 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.