Fair Value Measurements - Recurring Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reconciliation of items measured at fair value on a recurring basis that used significant unobservable inputs (Level 3)
Balance at the beginning of the period	$ 15	$ 12	$ 15	$ 11
Total gains or losses included in other comprehensive income	0	0	0	1
Balance at the end of the period	$ 15	$ 12	$ 15	$ 12