Employee Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended	3 Months Ended			6 Months Ended	3 Months Ended
	Jun. 30, 2012 Pension Plan	Jun. 30, 2011 Pension Plan	Jun. 30, 2012 Pension Plan	Mar. 31, 2011 Pension Plan Predecessor	Jun. 30, 2012 Post-Retirement Benefit Plan	Jun. 30, 2011 Post-Retirement Benefit Plan	Jun. 30, 2012 Post-Retirement Benefit Plan	Mar. 31, 2011 Post-Retirement Benefit Plan Predecessor
Components of net periodic benefit (income) expense
Service cost	$ 15	$ 13	$ 29	$ 14	$ 2	$ 1	$ 4	$ 2
Interest cost	97	108	196	104	37	41	73	41
Expected return on plan assets	(144)	(139)	(288)	(133)	(10)	(12)	(21)	(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)	$ (18)	$ (63)	$ 10	$ 29	$ 30	$ 56	$ 16