Compensation and Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Compensation And Benefit Plans Disclosure [Abstract]
Employer contribution to 401 (k) defined contribution savings plan	$ 99		$ 80	$ 83
Amounts recognized in the consolidated balance sheets consist of:
Long-term liabilities	(2,912)		(2,260)
Pension Plans
Compensation And Benefit Plans Disclosure [Abstract]
Expected contribution by employer in the next fiscal year	286
Percentage of decline in market value of investments held in trust (as a percent)					35.00%
Change in benefit obligation
Projected benefit obligation at beginning of year	4,080		3,688
Service cost	165		149
Interest cost	210		210
Amendments	0		6
Actuarial loss	327		210
Benefits paid	(289)		(183)
Projected benefit obligation at end of year	4,493		4,080	3,688
Change in plan assets
Fair value of plan assets at the beginning of the year	3,235		2,857
Actual return on plan assets	61		434
Employer contributions	146		127
Benefits paid	(289)		(183)
Fair value of plan assets at the end of the year	3,153		3,235	2,857
Funded status at end of year	(1,340)		(845)
Amounts recognized in the consolidated balance sheets consist of:
Current liabilities	(11)		(12)
Long-term liabilities	(1,329)		(833)
Total	(1,340)		(845)
Amounts recognized in accumulated other comprehensive loss consist of:
Prior service cost	1		1
Net loss	139		116
Total	140		117
Defined Benefit Plan, Amounts Recognized as Regulatory Asset (Liability) [Abstract]
Prior service credit	34		40
Net loss	955		500
Total	989		540
Total not yet recognized as expense	1,129		657
Accumulated benefit obligation at end of year	4,157		3,736
Pension plans with an accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	4,493		4,080
Accumulated benefit obligation	4,157		3,736
Fair value of plan assets	3,153		3,235
Weighted-average assumptions used to determine obligations at end of year:
Discount rate (as a percent)	4.50%		5.25%
Rate of compensation increase (as a percent)	4.50%		5.00%
Expense components are:
Service cost	165		149	124
Interest cost	210		210	207
Expected return on plan assets	(238)		(210)	(169)
Amortization of prior service cost (credit)	7		8	11
Amortization of net loss	28		22	61
Total expense	172		179	234
Regulatory adjustment - deferred	(28)		(52)	(94)
Total expense recognized	144		127	140
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net loss (gain)	35		30	17
Amortization of prior service (cost) credit	0		(1)	(1)
Amortization of net loss	(13)		(10)	(11)
Total recognized in other comprehensive (income) loss	22		19	5
Total recognized in expense and other comprehensive income	166		146	145
Estimated net (gain) loss that will be amortized to expense in next fiscal year	67
Estimated prior service cost (credit) that will be amortized to expense in next fiscal year	4
Estimated net (gain) loss that will be reclassified in next fiscal year from accumulated other comprehensive loss	17
Weighted-average assumptions used to determine expense:
Discount rate (as a percent)	5.25%		6.00%	6.25%
Rate of compensation increase (as a percent)	5.00%		5.00%	5.00%
Expected return on plan assets (as a percent)	7.50%		7.50%	7.50%
Benefit payments expected to be paid, net:
Estimated future benefit payments, 2012	302
Estimated future benefit payments, 2013	310
Estimated future benefit payments, 2014	316
Estimated future benefit payments, 2015	329
Estimated future benefit payments, 2016	338
Estimated future benefit payments, 2017-2021	1,738
Postretirement Benefits Other Than Pensions
Compensation And Benefit Plans Disclosure [Abstract]
Expected contribution by employer in the next fiscal year	65
Percentage of decline in market value of investments held in trust (as a percent)					33.00%
Change in benefit obligation
Projected benefit obligation at beginning of year	2,425		2,110
Service cost	43		37
Interest cost	121		127
Amendments	0		23
Actuarial loss	47		216
Plan participants' contributions	18		17
Medicare Part D subsidy received	5		5
Benefits paid	(106)		(110)
Projected benefit obligation at end of year	2,553		2,425	2,110
Change in plan assets
Fair value of plan assets at the beginning of the year	1,606		1,459
Actual return on plan assets	11		175
Employer contributions	36		60
Plan participants' contributions	18		17
Medicare Part D subsidy received	5		5
Benefits paid	(106)		(110)
Fair value of plan assets at the end of the year	1,570		1,606	1,459
Funded status at end of year	(983)		(819)
Amounts recognized in the consolidated balance sheets consist of:
Current liabilities	(19)		(20)
Long-term liabilities	(964)		(799)
Total	(983)		(819)
Amounts recognized in accumulated other comprehensive loss consist of:
Prior service cost	8		7
Net loss	27		28
Total	35		35
Defined Benefit Plan, Amounts Recognized as Regulatory Asset (Liability) [Abstract]
Prior service credit	(125)		(161)
Net loss	839		718
Total	714		557
Total not yet recognized as expense	749		592
Weighted-average assumptions used to determine obligations at end of year:
Discount rate (as a percent)	4.75%		5.50%
Rate assumed for following year (as a percent)	9.50%		9.75%
Ultimate rate (as a percent)	5.25%		5.50%
Year ultimate rate reached	2019		2019
Expense components are:
Service cost	43		37	30
Interest cost	121		127	122
Expected return on plan assets	(111)		(101)	(81)
Amortization of prior service cost (credit)	(36)		(38)	(34)
Amortization of net loss	27		36	45
Total expense	44		61	82
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net loss (gain)	(1)		13	(8)
Prior service cost (credit)	0		11	(3)
Amortization of prior service (cost) credit	1		2	2
Amortization of net loss	(1)		(1)	(1)
Total recognized in other comprehensive (income) loss	(1)		25	(10)
Total recognized in expense and other comprehensive income	43		86	72
Estimated net (gain) loss that will be amortized to expense in next fiscal year	46
Estimated prior service cost (credit) that will be amortized to expense in next fiscal year	(35)
Estimated net (gain) loss that will be reclassified in next fiscal year from accumulated other comprehensive loss	2
Estimated prior service cost (credit) that will be reclassified in next fiscal year from accumulated other comprehensive loss	0
Weighted-average assumptions used to determine expense:
Discount rate (as a percent)	5.50%		6.00%	6.25%
Expected return on plan assets (as a percent)	7.00%		7.00%	7.00%
Assumed health care cost trend rates:
Current year (as a percent)	9.75%		8.25%	8.75%
Ultimate rate (as a percent)	5.50%		5.50%	5.50%
Year ultimate rate reached	2019		2016	2016
Benefit payments expected to be paid before subsidy:
Estimated future benefit payments before subsidy, 2012	100	[1]
Estimated future benefit payments before subsidy, 2013	108	[1]
Estimated future benefit payments before subsidy, 2014	117	[1]
Estimated future benefit payments before subsidy, 2015	126	[1]
Estimated future benefit payments before subsidy, 2016	136	[1]
Estimated future benefit payments before subsidy, 2017-2021	809	[1]
Benefit payments expected to be paid, net:
Estimated future benefit payments, 2012	94
Estimated future benefit payments, 2013	102
Estimated future benefit payments, 2014	110
Estimated future benefit payments, 2015	119
Estimated future benefit payments, 2016	128
Estimated future benefit payments, 2017-2021	755
Effect of a one-percentage-point increase on accumulated benefit obligation	297
Effect of a one-percentage-point increase on total of service and interest cost components	16
Effect of a one-percentage-point decrease on accumulated benefit obligation	(247)
Effect of a one-percentage-point decrease on total of service and interest cost components	$ (13)
Eligibility age (in years)	55
Minimum service period for eligibility (in years)	10

[1] Medicare Part D prescription drug benefits