Income Tax Provision - Provision for Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Current
Federal									$ (25)	$ (24)	$ (15)
State									(15)	(3)	41
Foreign									9	8	6
Total current									(31)	(19)	32
Deferred
Federal									644	460	721
State									117	54	69
Foreign									(1)	2	2
Total deferred									760	516	792
Provision for income taxes	$ 155	$ 185	$ 176	$ 213	$ 182	$ 113	$ 149	$ 53	$ 729	$ 497	$ 824