Postretirement Benefits (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Y plan	Dec. 31, 2010 plan	Dec. 31, 2009
Change in projected benefit obligation:
Benefit obligation at beginning of period	$ 400	$ 344	$ 326
Service cost	17	15	15
Interest cost	23	21	19
Amendments	1	1	3
Actuarial loss (gain)	54	25	(12)
Benefits paid	(7)	(6)	(4)
Impact due to settlement	0	0	(3)
Benefit obligation at end of period	488	400	344
Change in plan assets:
Fair value of plan assets at beginning of period	0
Fair value of plan assets at end of period	348	0
Funded status at end of period	(140)	(72)	(65)
Amounts recognized in the Consolidated Statement of Financial Position:
Current liabilities	(1)	0	0
Noncurrent liabilities	(139)	(72)	(65)
Net amount recognized	(140)	(72)	(65)
Accumulated benefit obligation at end of period	363	297	252
Amounts included in accumulated other comprehensive income, before tax, not yet recognized as components of net periodic benefit cost:
Net actuarial loss	173	110	104
Prior service cost	6	5	5
Net amount not yet recognized	179	115	109
Components of net periodic benefit cost:
Service cost	17	15	15
Interest cost	23	21	19
Expected return on plan assets	(27)	(25)	(24)
Amortization of prior service cost	1	1	0
Recognized net actuarial loss	6	3	3
Settlement gain	0	0	(1)
Net periodic benefit expense before allocation to affiliates	20.0	15.0	12.0
Period for which the averaging method is used to determine the market-related value of plan assets (in years)	4
Period under which asset gains or losses that result from returns that differ from our long-term rate of return assumption are recognized in the market-related value of assets on a level basis (in years)	4
Amortization period of experience losses on plan assets (in years)	15
Amount recognized in other comprehensive income for pension plans:
Amortization of net actuarial loss	(6)	(4)
Amortization of prior service cost	(1)	0
Net actuarial loss arising during the year	69	9
Amendments	1	1
Total recognized in other comprehensive income	63	6
Amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost during next fiscal year
Amortization of net actuarial loss	11
Amortization of prior service cost	1
Number of new plan participants	7	4
Employee pension plan
Change in plan assets:
Fair value of plan assets at beginning of period	328	279	218
Actual return (loss) on plan assets	12	41	51
Employer contributions	15	13	14
Benefits paid	(7)	(5)	(4)
Fair value of plan assets at end of period	$ 348	$ 328	$ 279