Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Accumulated other comprehensive income (loss), start of period	$ (3,898)	$ (6,433)
Other comprehensive income (loss) before reclassifications	32	(367)
Amounts reclassified from accumulated other comprehensive (income) loss	65	131
Other comprehensive income (loss)	97	(236)
Accumulated other comprehensive income (loss), end of period	(3,801)	(6,669)
Foreign currency translation
Accumulated other comprehensive income (loss), start of period	176	456
Other comprehensive income (loss) before reclassifications	40	(366)
Amounts reclassified from accumulated other comprehensive (income) loss	0	0
Other comprehensive income (loss)	40	(366)
Accumulated other comprehensive income (loss), end of period	216	90
Pension and other postretirement benefits
Accumulated other comprehensive income (loss), start of period	(4,152)	(6,914)
Other comprehensive income (loss) before reclassifications	0	15
Amounts reclassified from accumulated other comprehensive (income) loss	80	121
Other comprehensive income (loss)	80	136
Accumulated other comprehensive income (loss), end of period	(4,072)	(6,778)
Derivative financial instruments
Accumulated other comprehensive income (loss), start of period	(5)	(42)
Other comprehensive income (loss) before reclassifications	(16)	(31)
Amounts reclassified from accumulated other comprehensive (income) loss	(5)	11
Other comprehensive income (loss)	(21)	(20)
Accumulated other comprehensive income (loss), end of period	(26)	(62)
Available-for-sale securities
Accumulated other comprehensive income (loss), start of period	83	67
Other comprehensive income (loss) before reclassifications	8	15
Amounts reclassified from accumulated other comprehensive (income) loss	(10)	(1)
Other comprehensive income (loss)	(2)	14
Accumulated other comprehensive income (loss), end of period	$ 81	$ 81