Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2011 Investment	Sep. 30, 2010	Sep. 30, 2011 Year Investment	Sep. 30, 2010	Dec. 31, 2010
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	$ 1,267		$ 1,267		$ 1,299
Number of securities	182		182
Total Fair Value	1,167		1,167		1,225
Total Unrealized Losses	115		115		49
Fixed maturities, fair value of hybrid securities	69		69
Net realized investment gains (losses), net	(2)	155	77	140
Gross realized investment gains	19	148	136	177
Gross realized investment losses	17	1	35	12
Impaired fixed-maturity matured securities	3	1	33	36
Investments securities total unrealized loss in an unrealized loss position for 12 months or more	4		4		5
Equity Securities
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	574		574		784
Total Fair Value	597		597		365
Total Unrealized Losses	97		97		29
Number of securities total unrealized loss in an unrealized loss position for 12 months or more	2		2		3
Investments securities total unrealized loss in an unrealized loss position for 12 months or more	1		1		1
Equity Securities | Three Largest Contributors
Gain (Loss) on Investments [Line Items]
Number of securities	3		3
Total Fair Value	125		125
Total Unrealized Losses	55		55
Equity Securities | Traded below cost for less than six months
Gain (Loss) on Investments [Line Items]
Number of securities	2		2
Equity Securities | Traded below cost for less than nine months
Gain (Loss) on Investments [Line Items]
Number of securities	1		1
Debt Securities
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	693		693		515
Total Fair Value	570		570		860
Total Unrealized Losses	18		18		20
Number of securities total unrealized loss in an unrealized loss position for 12 months or more	13		13		17
Investments securities total unrealized loss in an unrealized loss position for 12 months or more	3		3		4
Debt Securities | Third Quarter
Gain (Loss) on Investments [Line Items]
Impaired fixed-maturity securities	4		4
Impaired fixed-maturity matured securities			3
Procter And Gamble Company And Exxon Mobile Corporation | Common Stock Investment
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	251		251
Fixed Income Securities
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	675		675
Fixed Income Securities | Corporate Bond Securities
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	455		455
Fixed Income Securities | Municipal Bonds
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	219		219
Common Stock Investment
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	$ 452		$ 452