Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Long duration fixed income [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation percentage	.50
Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation percentage	.30
Other investments [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation percentage	.20
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of benefit plans	4
Contributions by employer	$ 59	$ 64
Benefits paid	38	62
Qualified Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of benefit plans	1
Contributions by employer	48	34
Nonqualified Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of benefit plans	3
Benefits paid	11	30
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer	7	6
Benefits paid	$ 7	$ 6
401(k) Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of benefit plans	2