Fair Value Measurements - Reconciliation of Changes in Level 3 Balances (Details) (Fair Value, Measurements, Recurring [Member], Level 3 [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 137
Realized/unrealized gains/(losses) [Abstract]
Other income, net (assets and liabilities, net)	(81)
Purchases, issues, sales and settlements [Abstract]
Settlements (assets and liabilites, net)	(56)
Ending balance	0
Unrealized gains/(losses) on instruments still held	$ 0