Short-Term Borrowings (Schedule of Short-term Debt) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Demand Notes	$ 3,375	$ 3,338
Federal Home Loan Bank, Advances, Short-term	4,550	2,950
Securities Sold under Agreements to Repurchase, Gross	2,004	774
Other Short-term Borrowings	84	0
Short-term borrowings	10,013	7,062
Non-derivative Cash Collateral Placed with Counterparties Associated with the Repurchase Agreements	17
Non-derivative Cash Collateral Received from Counterparties Associated with the Repurchase Agreements.	4
Unsecured Debt [Member]
Short-term Debt [Line Items]
Demand Notes	3,375	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	3,459	3,338
Secured Debt [Member]
Short-term Debt [Line Items]
Demand Notes	0	0
Federal Home Loan Bank, Advances, Short-term	4,550	2,950
Securities Sold under Agreements to Repurchase, Gross	2,004	774
Other Short-term Borrowings	0	0
Short-term borrowings	6,554	$ 3,724
U.S. Treasury and Federal Agency Securities Sold under Agreements to Repurchase, Mature within the Next 30 days	383
Mortgage-backed Residential Securities Sold under Agreements to Repurchase, Mature within 30 days	1,600
Secured Debt [Member] | Maturity up to 30 days [Member]
Short-term Debt [Line Items]
Securities Sold under Agreements to Repurchase, Gross	$ 2,000