Short-Term Borrowings (Schedule of Short-term Debt) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Demand Notes	$ 3,576	$ 3,369
Federal Home Loan Bank, Advances, Short-term	1,950	4,000
Securities Sold under Agreements to Repurchase, Gross	468	648
Other Short-term Borrowings	0	84
Short-term borrowings	5,994	8,101
Non-derivative Cash Collateral Placed with Counterparties Associated with the Repurchase Agreements	7	21
Unsecured Debt [Member]
Short-term Debt [Line Items]
Demand Notes	3,576	3,369
Federal Home Loan Bank, Advances, Short-term	0	0
Securities Sold under Agreements to Repurchase, Gross	0	0
Other Short-term Borrowings	0	84
Short-term borrowings	3,576	3,453
Secured Debt [Member]
Short-term Debt [Line Items]
Demand Notes	0	0
Federal Home Loan Bank, Advances, Short-term	1,950	4,000
Securities Sold under Agreements to Repurchase, Gross	468	648
Other Short-term Borrowings	0	0
Short-term borrowings	2,418	$ 4,648
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	369
Secured Debt [Member] | Maturity 31 to 60 Days [Member]
Short-term Debt [Line Items]
Mortgage-backed Residential Securities Sold under Agreements to Repurchase, Maturity Period	$ 99