Summary of Funded Status of Pension Plans (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee Benefit Plans [Abstract]
Benefit obligation at end of prior year	$ 600	$ 236
Service cost	5	3	2
Interest cost	27	17	12
Plan amendments	1
Actuarial loss	58	52
Net benefits paid	(21)	(14)
Assumed benefit obligation of acquired entities		306
Benefit obligation at end of current year	670	600	236
Fair value of assets at end of prior year	412	173
Actual return on plan assets	56	22
Employer contributions	18	24
Net benefits paid	(21)	(14)
Acquired fair value of plan assets of acquired entities		207
Fair value of assets at end of current year	465	412	173
Total unfunded status at end of year (recognized in other non-current liabilities in the Consolidated Balance Sheets)	$ (205)	$ (188)