Derivative Financial Instruments Derivative Instruments, Gain (Loss) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest and Fee Income, Loans and Leases Held-in-portfolio		$ 1,697	$ 1,398
Interest Expense, Long-term Debt		(125)	(74)
Interest Expense, Deposits		(249)	(131)
Trading Gain (Loss)		60	42
Total Amounts of Line Items Presented in the Consolidated Statements of Income		1,572	1,324
Loans Held-For-Investment [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest and Fee Income, Loans and Leases Held-in-portfolio		1,697	1,398
Long-term Debt [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest Expense, Long-term Debt		(125)	(74)
Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Related to Interest Settlements on Derivatives		(4)	3
Derivative, Gain (Loss) on Derivative, Net		66	(72)
Gain (Loss) on Fair Value Hedges Recognized in Earnings		(71)	69
Net Income (Expense) Recognized on Hedges		(9)	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	0
Derivative, Gain (Loss) on Derivative, Net		0	0
Gain (Loss) on Fair Value Hedges Recognized in Earnings		0	0
Net Income (Expense) Recognized on Hedges		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		(4)	3
Derivative, Gain (Loss) on Derivative, Net		66	(72)
Gain (Loss) on Fair Value Hedges Recognized in Earnings	[1]	(71)	69
Net Income (Expense) Recognized on Hedges		(9)	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		(39)	(1)
Net Income (Expense) Recognized on Hedges		(39)	(1)
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]	(39)	(1)
Net Income (Expense) Recognized on Hedges		(39)	(1)
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
Net Income (Expense) Recognized on Hedges		$ 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.