Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended	3 Months Ended	9 Months Ended			3 Months Ended	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Fixed Maturities security	Sep. 30, 2014 Fixed Maturities security	Sep. 30, 2013 Fixed Maturities security	Dec. 31, 2013 Fixed Maturities security	Sep. 30, 2014 Equity Securities security	Sep. 30, 2014 Equity Securities security	Dec. 31, 2013 Equity Securities	Sep. 30, 2014 Procter And Gamble Company, Exxon Mobile Corporation And Chevron Corporation [Member]	Sep. 30, 2014 Common Stock
Gain (Loss) on Investments [Line Items]
Number of securities											7
Unrealized investment gains due to a net gain position			$ 627	$ 627		$ 558	$ 1,976	$ 1,976	$ 1,856	$ 579
Largest equity holdings to total equity portfolio	3.10%
Largest equity holdings to total portfolio	1.00%
Number Of Securities Other Than Temporary Impairment Losses1			0	1	7		0	3
Number Of Securities Continuous Unrealized Loss Position More Than Twelve Months			212	212		40	4	4
Unrealized losses 12 months or more (equity investment less than $500,000)	$ 25	$ 5	$ 20	$ 20		$ 5	$ 5	$ 5	$ 0
Fixed maturity investments, Percentage of amortized costs	70.00%	70.00%