Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	$ (2,001)	$ (795)	$ (2,017)	$ (802)
Other comprehensive income (loss) before reclassifications	11	8	0	9
Amounts reclassified from accumulated other comprehensive income	31	8	58	14
Other comprehensive income	42	16	58	23
Balance at the end of the period	(1,959)	(779)	(1,959)	(779)
Defined benefit plan | Pension plans
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(1,696)	(666)	(1,720)	(669)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income	28	5	52	8
Other comprehensive income	28	5	52	8
Balance at the end of the period	(1,668)	(661)	(1,668)	(661)
Defined benefit plan | Post-retirement benefit plans
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(269)	(119)	(272)	(122)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income	3	3	6	6
Other comprehensive income	3	3	6	6
Balance at the end of the period	(266)	(116)	(266)	(116)
Foreign currency translation adjustment and other
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(36)	(10)	(25)	(11)
Other comprehensive income (loss) before reclassifications	11	8	0	9
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive income	11	8	0	9
Balance at the end of the period	$ (25)	$ (2)	$ (25)	$ (2)