Pension and Other Postretirement Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension And Other Postretirement Footnote Text Details [Abstract]
Increase (decrease) to postretirement benefits liability adjustment pre-tax	$ 129	$ 558	$ 301
Increase (decrease) to postretirement benefits liability adjustement after-tax	92	360	189
Pension Benefits [Member]
Change in benefit obligation [Abstract]
Benefit obligation, January 1	5,067	4,691
Service cost	3	2	2
Interest cost	198	228	240
Loss from past experience	283	453
Benefits paid from plan assets	(256)	(273)
Benefits paid - other	(28)	(34)
Benefit obligation, December 31	5,267	5,067	4,691
Change in plan assets [Roll Forward]
Fair value of plan assets, January 1	3,298	3,163
Actual return on plan assets	370	156
Benefits paid	(256)	(273)
Contributions	253	252
Fair value of plan assets, December 31	3,665	3,298	3,163
Funded Status	(1,602)	(1,769)
Postretirement benefits liability adjustment included in AOCI table details [Abstract]
Unrecognized net gain (loss)	(2,450)	(2,331)
Unrecognized prior service cost	(5)	(5)
Postretirement benefits liabilty adjustment	(2,455)	(2,336)
Components of net pension cost and other postretirement benefits cost tables detail [Abstract]
Service cost	3	2	2
Interest cost	198	228	240
Expected long-term return on plan assets	(270)	(267)	(253)
Amortization of net loss from past experience	58	38	28
Settlement loss	6	0	0
Net pension cost	(5)	1	17
Pension And Other Postretirement Footnote Text Details [Abstract]
Defined Benefit Plan Accumulated Benefit Obligations	5,300	5,100
Expected minimum required funding contributions next year	For 2013, the Company expects to make minimum required and voluntary contributions totaling approximately $250 million.
Expected pre-tax gains (losses) related to amortization of prior experience	(75)
Weighted average amortization period for amortization of past experience	28 years
Other Postretirement Benefits [Member]
Change in benefit obligation [Abstract]
Benefit obligation, January 1	452	444
Service cost	2	2	1
Interest cost	16	20	22
Loss from past experience	(2)	16
Benefits paid from plan assets	(3)	(2)
Benefits paid - other	(23)	(28)
Benefit obligation, December 31	442	452	444
Change in plan assets [Roll Forward]
Fair value of plan assets, January 1	22	23
Actual return on plan assets	1	1
Benefits paid	(3)	(2)
Contributions		0
Fair value of plan assets, December 31	20	22	23
Funded Status	(422)	(430)
Postretirement benefits liability adjustment included in AOCI table details [Abstract]
Unrecognized net gain (loss)	(28)	(30)
Unrecognized prior service cost	23	35
Postretirement benefits liabilty adjustment	(5)	5
Components of net pension cost and other postretirement benefits cost tables detail [Abstract]
Service cost	2	2	1
Interest cost	16	20	22
Expected long-term return on plan assets	(1)	(1)	(1)
Amortization of prior service cost	(12)	(16)	(18)
Net pension cost	5	5	4
Results of a 1% increase or decrease in healthcare benefits estimate range table details [Abstract]
Effect of increase on postretirement benefit obligation	12
Effect of decrease on postretirement benefit obligation	10
Retiree Health Benefits [Member]
Pension And Other Postretirement Footnote Text Details [Abstract]
Defined Benefit Plan Accumulated Benefit Obligations	294	302
Expected pre-tax gains (losses) related to amortization of prior experience	0
Weighted average amortization period for amortization of past experience	11 years
Expected pre-tax gains (losses) related to amortization of net prior service cost	9
Weighted Average Remaining amortization period for prior service costs	2 years 6 months
Estimated rate of future increases in the per capita cost of health care benefits	7.50%
Estimated decrease in rate per year of future increases in the per capita cost of health care benefits	decreasing by 0.5% per year
Estimated rate of future increases in the per capita cost of health care benefits in 2018 and beyond	5.00%
Year that estimated rate of future cost of health care is realized	2018
Retiree Life Insurance Benefits [Member]
Pension And Other Postretirement Footnote Text Details [Abstract]
Defined Benefit Plan Accumulated Benefit Obligations	$ 148	$ 150