Stockholders' Equity 1 (Details) (USD $) In Millions, except Per Share data, 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
Cash dividends
Declaration date	Feb. 05, 2015	Nov. 06, 2014	Jul. 31, 2014	May 15, 2014	Feb. 05, 2014	Nov. 06, 2013	Aug. 01, 2013	May 09, 2013
Dividend per share (in dollars per share)	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25
Record date	Feb. 19, 2015	Nov. 20, 2014	Aug. 21, 2014	May 29, 2014	Feb. 20, 2014	Nov. 21, 2013	Aug. 22, 2013	May 23, 2013
Total amount	$ 111	$ 111	$ 111	$ 111	$ 112	$ 113	$ 114	$ 114	$ 444	$ 453	$ 463
Payment date	Mar. 17, 2015	Dec. 09, 2014	Sep. 09, 2014	Jun. 17, 2014	Mar. 18, 2014	Dec. 10, 2013	Sep. 10, 2013	Jun. 11, 2013