Gross Unrealized Losses and Fair Values for Investments in Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months, Fair Value	$ 2,021	$ 3,178
Less than 12 Months, Unrealized Loss	(48)	(111)
12 Months or Greater, Fair Value	166	42
12 Months or Greater, Unrealized Loss	(10)	(3)
Total Fair Value	2,187	3,220
Total Unrealized Loss	(58)	(114)
Foreign government bonds
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months, Fair Value	397	302
Less than 12 Months, Unrealized Loss	(4)	(11)
12 Months or Greater, Fair Value	9	6
12 Months or Greater, Unrealized Loss	(2)	0
Total Fair Value	406	308
Total Unrealized Loss	(6)	(11)
Corporate debt securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months, Fair Value	827	2,160
Less than 12 Months, Unrealized Loss	(24)	(97)
12 Months or Greater, Fair Value	157	17
12 Months or Greater, Unrealized Loss	(8)	(1)
Total Fair Value	984	2,177
Total Unrealized Loss	(32)	(98)
Agency residential mortgage-backed securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months, Fair Value	704	716
Less than 12 Months, Unrealized Loss	(3)	(3)
12 Months or Greater, Fair Value	0	19
12 Months or Greater, Unrealized Loss	0	(2)
Total Fair Value	704	735
Total Unrealized Loss	(3)	(5)
Marketable equity securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months, Fair Value	93
Less than 12 Months, Unrealized Loss	(17)
12 Months or Greater, Fair Value	0
12 Months or Greater, Unrealized Loss	0
Total Fair Value	93
Total Unrealized Loss	$ (17)