Investments (Fair Values And Gross Unrealized Losses By Credit Rating Category Of Corporate Obligations) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Total Fair Value	$ 1,558	$ 2,387
Total Unrealized Loss	(226)	(478)
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Fair Value	305
Total Unrealized Loss	(31)
Aaa [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Fair Value	4
Aa [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Fair Value	39
A [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Fair Value	130
Total Unrealized Loss	(6)
Baa [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Fair Value	107
Total Unrealized Loss	(9)
Below Investment Grade [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Fair Value	13
Total Unrealized Loss	(4)
Not Rated [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total Fair Value	12
Total Unrealized Loss	$ (12)