Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net Income	$ 532	$ 487	$ 486
Other comprehensive income (loss), net of tax:
Benefit obligations, net of tax of $(4), $4 and $(1), respectively	(10)	5	(2)
Net unrealized gains on investments during the period, net of taxes of $—, $— and $—, respectively	0	1	0
Other comprehensive income (loss)	(10)	6	(2)
Comprehensive income	$ 522	$ 493	$ 484