Employee Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended	9 Months Ended	3 Months Ended			6 Months Ended	9 Months Ended	3 Months Ended
	Sep. 30, 2012 Pension Plan	Sep. 30, 2011 Pension Plan	Sep. 30, 2011 Pension Plan	Sep. 30, 2012 Pension Plan	Mar. 31, 2011 Pension Plan Predecessor	Sep. 30, 2012 Post-Retirement Benefit Plan	Sep. 30, 2011 Post-Retirement Benefit Plan	Sep. 30, 2011 Post-Retirement Benefit Plan	Sep. 30, 2012 Post-Retirement Benefit Plan	Mar. 31, 2011 Post-Retirement Benefit Plan Predecessor
Components of net periodic benefit (income) expense
Service cost	$ 15	$ 14	$ 27	$ 44	$ 14	$ 2	$ 2	$ 3	$ 6	$ 2
Interest cost	97	106	214	293	104	37	42	83	110	41
Expected return on plan assets	(144)	(139)	(278)	(432)	(133)	(10)	(13)	(25)	(31)	(13)
Recognition of prior service cost					(6)					(24)
Recognition of net actuarial loss					31					10
Net periodic pension (income) expense and post-retirement benefit expense	$ (32)	$ (19)	$ (37)	$ (95)	$ 10	$ 29	$ 31	$ 61	$ 85	$ 16