Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	$ (1,907)	$ (2,001)	$ (1,934)	$ (2,017)
Other comprehensive income (loss) before reclassifications	(4)	11	(5)	0
Amounts reclassified from accumulated other comprehensive income	30	31	58	58
Net current-period other comprehensive income	26	42	53	58
Balance at the end of the period	(1,881)	(1,959)	(1,881)	(1,959)
Defined benefit plan | Pension plans
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(1,690)	(1,696)	(1,715)	(1,720)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income	27	28	52	52
Net current-period other comprehensive income	27	28	52	52
Balance at the end of the period	(1,663)	(1,668)	(1,663)	(1,668)
Defined benefit plan | Post-retirement benefit plans
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(177)	(269)	(180)	(272)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income	3	3	6	6
Net current-period other comprehensive income	3	3	6	6
Balance at the end of the period	(174)	(266)	(174)	(266)
Foreign currency translation adjustment and other
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(40)	(36)	(39)	(25)
Other comprehensive income (loss) before reclassifications	(4)	11	(5)	0
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Net current-period other comprehensive income	(4)	11	(5)	0
Balance at the end of the period	$ (44)	$ (25)	$ (44)	$ (25)