Derivative Financial Instruments Derivative Instruments, Gain (Loss) (Additional Information) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liability, Fair Value, Gross Liability		$ 3,499		$ 3,499		$ 4,442
Interest Rate Contract [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		(16)	$ 27	(17)	$ 68
Loans Held-For-Investment [Member] | Interest Rate Contract [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	[1]	(16)	27	(17)	68
Loans Held-For-Investment [Member] | Interest Rate Contract [Member] | Interest Income [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net		$ (61)	$ 76	$ (225)	$ 51

[1] 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.