Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	$ (1,934)	$ (2,017)
Other comprehensive income (loss) before reclassifications	(1)	(11)
Amounts reclassified from accumulated other comprehensive income	28	27
Net current-period other comprehensive income	27	16
Balance at the end of the period	(1,907)	(2,001)
Defined benefit plan | Pension plans
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(1,715)	(1,720)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	25	24
Net current-period other comprehensive income	25	24
Balance at the end of the period	(1,690)	(1,696)
Defined benefit plan | Post-retirement benefit plans
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(180)	(272)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	3	3
Net current-period other comprehensive income	3	3
Balance at the end of the period	(177)	(269)
Foreign currency translation adjustment and other
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(39)	(25)
Other comprehensive income (loss) before reclassifications	(1)	(11)
Amounts reclassified from accumulated other comprehensive income	0	0
Net current-period other comprehensive income	(1)	(11)
Balance at the end of the period	$ (40)	$ (36)