Short-Term Borrowings (Schedule of Short-term Debt) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Demand Notes	$ 3,374	$ 3,338
Federal Home Loan Bank, Advances, Short-term	400	2,950
Securities Sold under Agreements to Repurchase, Gross	1,520	774
Other Short-term Borrowings	84	0
Short-term borrowings	5,378	7,062
Non-derivative Cash Collateral Received from Counterparties Associated with the Repurchase Agreements.	4
Unsecured Debt [Member]
Short-term Debt [Line Items]
Demand Notes	3,374	3,338
Federal Home Loan Bank, Advances, Short-term	0	0
Securities Sold under Agreements to Repurchase, Gross	0	0
Other Short-term Borrowings	84	0
Short-term borrowings	3,458	3,338
Secured Debt [Member]
Short-term Debt [Line Items]
Demand Notes	0	0
Federal Home Loan Bank, Advances, Short-term	400	2,950
Securities Sold under Agreements to Repurchase, Gross	1,520	774
Other Short-term Borrowings	0	0
Short-term borrowings	1,920	$ 3,724
Secured Debt [Member] | Maturity up to 30 days [Member]
Short-term Debt [Line Items]
Mortgage-backed Residential Securities Sold under Agreements to Repurchase, Maturity Period	1,371
Secured Debt [Member] | Maturity Greater than 90 Days [Member]
Short-term Debt [Line Items]
Mortgage-backed Residential Securities Sold under Agreements to Repurchase, Maturity Period	$ 149