Stockholders' Equity 1 (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Cash dividends
Declaration date	Feb. 03, 2016	Nov. 05, 2015	Aug. 06, 2015	May 05, 2015	Feb. 05, 2015	Nov. 06, 2014	Jul. 31, 2014	May 15, 2014
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. 18, 2016	Nov. 19, 2015	Aug. 27, 2015	May 28, 2015	Feb. 19, 2015	Nov. 20, 2014	Aug. 21, 2014	May 29, 2014
Total amount	$ 104	$ 105	$ 110	$ 110	$ 111	$ 111	$ 111	$ 111	$ 429	$ 444	$ 453
Payment date	Mar. 15, 2016	Dec. 08, 2015	Sep. 15, 2015	Jun. 16, 2015	Mar. 17, 2015	Dec. 09, 2014	Sep. 09, 2014	Jun. 17, 2014