Schedule of Details of Dividend Payments (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Record Date	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Payment Date	Apr. 24, 2015	Jan. 30, 2015	Oct. 31, 2014	Jul. 25, 2014	Apr. 25, 2014	Jan. 31, 2014
Amount per Share	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.27	$ 0.27
Total Amount	$ 42	$ 42	$ 43	$ 43	$ 42	$ 42