Accumulated Other Comprehensive Loss (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated other comprehensive income (loss) by component
Balance at December 31, 2013	$ (802)	$ (1,701)
Other comprehensive income (loss) before reclassifications	(1,284)	840
Amounts reclassified from accumulated other comprehensive income	69	59
Net current-period other comprehensive income (loss)	(1,215)	899	(689)
Balance at December 31, 2014	(2,017)	(802)	(1,701)
Foreign Currency Translation Adjustment and Other
Accumulated other comprehensive income (loss) by component
Balance at December 31, 2013	(11)	(13)
Other comprehensive income (loss) before reclassifications	(15)	1
Amounts reclassified from accumulated other comprehensive income	1	1
Net current-period other comprehensive income (loss)	(14)	2
Balance at December 31, 2014	(25)	(11)
Defined Benefit Plans | Pension Plans
Accumulated other comprehensive income (loss) by component
Balance at December 31, 2013	(669)	(1,399)
Other comprehensive income (loss) before reclassifications	(1,107)	675
Amounts reclassified from accumulated other comprehensive income	56	55
Net current-period other comprehensive income (loss)	(1,051)	730
Balance at December 31, 2014	(1,720)	(669)
Defined Benefit Plans | Post-Retirement Benefit Plans
Accumulated other comprehensive income (loss) by component
Balance at December 31, 2013	(122)	(289)
Other comprehensive income (loss) before reclassifications	(162)	164
Amounts reclassified from accumulated other comprehensive income	12	3
Net current-period other comprehensive income (loss)	(150)	167
Balance at December 31, 2014	$ (272)	$ (122)