Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) Net Of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax		$ (2,980)
Other comprehensive income (loss) before reclassifications		(56)
Amounts reclassified from accumulated other comprehensive income (loss)	(20)	(54)
Other Comprehensive Income (Loss), Net of Tax		(110)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(3,090)	(3,090)
Pension and retiree medical liability [Member]
Accumulated Other Comprehensive Income (Loss) Net Of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax		(2,322)
Other comprehensive income (loss) before reclassifications		0
Amounts reclassified from accumulated other comprehensive income (loss)		(66)
Other Comprehensive Income (Loss), Net of Tax		(66)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(2,388)	(2,388)
Unrealized gain (loss) on investments [Member]
Accumulated Other Comprehensive Income (Loss) Net Of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax		(1)
Other comprehensive income (loss) before reclassifications		0
Amounts reclassified from accumulated other comprehensive income (loss)		0
Other Comprehensive Income (Loss), Net of Tax		0
Accumulated Other Comprehensive Income (Loss), Net of Tax	(1)	(1)
Derivative financial instruments [Member]
Accumulated Other Comprehensive Income (Loss) Net Of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax		15
Other comprehensive income (loss) before reclassifications		(56)
Amounts reclassified from accumulated other comprehensive income (loss)	13	12
Other Comprehensive Income (Loss), Net of Tax		(44)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(29)	(29)
Income tax benefit (expense) [Member]
Accumulated Other Comprehensive Income (Loss) Net Of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax		(672)
Other comprehensive income (loss) before reclassifications		0
Amounts reclassified from accumulated other comprehensive income (loss)		0
Other Comprehensive Income (Loss), Net of Tax		0
Accumulated Other Comprehensive Income (Loss), Net of Tax	(672)	(672)
Prior Service Cost [Member] | Pension and retiree medical liability [Member]
Accumulated Other Comprehensive Income (Loss) Net Of Tax [Roll Forward]
Amounts reclassified from accumulated other comprehensive income (loss)	(54)	(108)
Actuarial Loss [Member] | Pension and retiree medical liability [Member]
Accumulated Other Comprehensive Income (Loss) Net Of Tax [Roll Forward]
Amounts reclassified from accumulated other comprehensive income (loss)	$ 21	$ 42