Derivative Financial Instruments (Summary of Collateral Positions with Counterparties) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Cash collateral to secure loss from counterparty related to derivative credit risk	$ 44	$ 41
Cash collateral posted related to derivative credit risk	386	607
Dealer Counterparties [Member]
Derivative [Line Items]
Cash collateral to secure loss from counterparty related to derivative credit risk	44	44
Derivatives in a gain position for which collateral has been received	46	42
Unsecured positions in a net gain with dealer counterparties after collateral postings	3	0
Cash collateral posted related to derivative credit risk	356	603
Derivatives in loss position for which collateral has been posted	357	610
Additional collateral required for decline in credit ratings below investment grade	4	10
Central Clearing Parties [Member]
Derivative [Line Items]
Cash collateral posted related to derivative credit risk	43	111
Derivatives in loss position for which collateral has been posted	43	7
Securities pledged to central clearing parties	$ 82	$ 0