Accumulated Other Comprehensive Loss (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	$ (2,017)	$ (802)
Other comprehensive income (loss) before reclassifications	(11)	1
Amounts reclassified from accumulated other comprehensive income	27	6
Other comprehensive income	16	7
Balance at the end of the period	(2,001)	(795)
Defined benefit plan | Pension plans
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(1,720)	(669)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	24	3
Other comprehensive income	24	3
Balance at the end of the period	(1,696)	(666)
Defined benefit plan | Post-retirement benefit plans
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(272)	(122)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	3	3
Other comprehensive income	3	3
Balance at the end of the period	(269)	(119)
Foreign currency translation adjustment and other
Accumulated other comprehensive income (loss) by component
Balance at the beginning of the period	(25)	(11)
Other comprehensive income (loss) before reclassifications	(11)	1
Amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive income	(11)	1
Balance at the end of the period	$ (36)	$ (10)