Derivative Financial Instruments (Summary of Collateral Positions with Counterparties) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivative [Line Items]
Cash collateral received from counterparties	$ 98	$ 44
Cash collateral posted to counterparties	262	386
Dealer Counterparties [Member]
Derivative [Line Items]
Cash collateral received from counterparties	79	44
Derivatives in a net gain position secured by that collateral	78	46
Unsecured positions in a net gain after collateral postings	2	3
Cash collateral posted to counterparties	247	356
Derivatives in a net loss position secured by that collateral	248	357
Additional collateral required for decline in credit ratings below investment grade	3	4
Central Clearing Parties [Member]
Derivative [Line Items]
Cash collateral received from counterparties	23	0
Derivatives in a net gain position secured by that collateral	21	26
Cash collateral posted to counterparties	26	43
Derivatives in a net loss position secured by that collateral	25	43
Securities pledged to central clearing parties	$ 124	$ 82