Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits, Excluding Tax Carryforwards and Interest and Penalties (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Balance at January 1	$ 91	$ 67	$ 63
Additions based on tax positions related to the current year	6	2	4
Additions for tax positions related to a prior year		31	5
Reductions for tax positions related to a prior year	(35)	(7)	(5)
Lapse of statute of limitations	(5)	(2)
Balance at December 31	$ 57	$ 91	$ 67