Changes in Equity (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Stockholders Equity Note [Line Items]
Beginning Balance	$ 1,958	$ 1,814	$ 1,838	$ 1,786
Total comprehensive income	12	113	142	145
Preferred stock dividends	(7)	(7)	(15)	(15)
Common stock dividends	(8)		(15)
Dividends attributable to noncontrolling interests	(8)	(1)	(8)	(3)
Stock compensation	4	7	9	15
Stock withheld for employee taxes	(1)	(1)	(1)	(3)
Ending Balance	1,950	1,925	1,950	1,925
To US Parent
Stockholders Equity Note [Line Items]
Beginning Balance	1,853	1,712	1,737	1,687
Total comprehensive income	10	110	136	137
Preferred stock dividends	(7)	(7)	(15)	(15)
Common stock dividends	(8)		(15)
Stock compensation	4	7	9	15
Stock withheld for employee taxes	(1)	(1)	(1)	(3)
Ending Balance	1,851	1,821	1,851	1,821
Attributable to Non- controlling Interests
Stockholders Equity Note [Line Items]
Beginning Balance	105	102	101	99
Total comprehensive income	2	3	6	8
Dividends attributable to noncontrolling interests	(8)	(1)	(8)	(3)
Ending Balance	$ 99	$ 104	$ 99	$ 104