Derivative Financial Instruments Derivative Instruments, Gain (Loss) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest and Fee Income, Loans and Leases Held-in-portfolio		$ 1,721	$ 1,476	$ 3,418	$ 2,874
Interest Expense, Long-term Debt		(150)	(83)	(275)	(157)
Interest Expense, Deposits		(269)	(159)	(519)	(291)
Trading Gain (Loss)		55	53	114	95
Total Amounts of Line Items Presented in the Consolidated Statements of Income		1,571	1,393	3,143	2,717
Loans Held-For-Investment [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest and Fee Income, Loans and Leases Held-in-portfolio		1,721	1,476	3,418	2,874
Long-term Debt [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest Expense, Long-term Debt		(150)	(83)	(275)	(157)
Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Related to Interest Settlements on Derivatives		(5)	(1)	(9)	(1)
Derivative, Gain (Loss) on Derivative, Net		159	(26)	225	(98)
Gain (Loss) on Fair Value Hedges Recognized in Earnings		(165)	24	(236)	93
Net Income (Expense) Recognized on Hedges		(11)	(3)	(20)	(4)
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		(5)	(1)	(9)	(1)
Derivative, Gain (Loss) on Derivative, Net		159	(26)	225	(98)
Gain (Loss) on Fair Value Hedges Recognized in Earnings	[1]	(165)	24	(236)	93
Net Income (Expense) Recognized on Hedges		(11)	(3)	(20)	(4)
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		(44)	(16)	(83)	(17)
Net Income (Expense) Recognized on Hedges		(44)	(16)	(83)	(17)
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]	(44)	(16)	(83)	(17)
Net Income (Expense) Recognized on Hedges		(44)	(16)	(83)	(17)
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

[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.