Debt Debt (Schedule of Long-term Debt Instruments) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Derivative, Amount of Hedged Item	$ 315	$ 331
Long-term Debt	54,128	66,234
Secured Debt	43,129	49,916
Fixed Income Interest Rate [Member]
Debt Instrument [Line Items]
Unsecured Debt	17,155	17,657
Trust preferred securities	2,568	2,600
Secured Debt	17,935	20,511
Variable Income Interest Rate [Member]
Debt Instrument [Line Items]
Unsecured Debt	1	375
Secured Debt	16,154	24,760
Unsecured Debt [Member]
Debt Instrument [Line Items]
Derivative, Amount of Hedged Item	326	334
Long-term Debt	$ 20,050	$ 20,966
Long-term Debt, Weighted Average Interest Rate	5.36%	5.40%
Secured Debt [Member]
Debt Instrument [Line Items]
Derivative, Amount of Hedged Item	$ (11)	$ (3)
Long-term Debt	$ 34,078	$ 45,268
Long-term Debt, Weighted Average Interest Rate	1.53%	1.18%
Variable Interest Entity Debt	$ 13,300	$ 20,300
Subordinated Debt [Member]
Debt Instrument [Line Items]
Unsecured Debt	1,400	1,100
Revolving secured funding facilities [Member]
Debt Instrument [Line Items]
Secured Debt	14,800	19,900
Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Secured Debt	$ 6,100	$ 5,400