Investments - Additional Information (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($) security
Gain (Loss) on Investments [Line Items]
Largest Single Common Stock Holding	$ 153
Largest equity holdings to total equity portfolio	3.20%
Largest equity holdings to total portfolio	1.00%
Unrealized losses 12 months or more (equity investment less than $500,000)	$ 24	$ 37
Number Of Securities Continuous Unrealized Loss Position More Than Twelve Months and Below 70 Percent of Amortized Cost | security	2	5
Number Of Securities Other Than Temporary Impairment Losses		20
Fixed maturity investments, Percentage of amortized costs	70.00%	70.00%
Fixed Maturities
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	$ 510	$ 431
Number Of Securities Other Than Temporary Impairment Losses1 | security	2
Number Of Securities Continuous Unrealized Loss Position More Than Twelve Months | security	44	69
Unrealized losses 12 months or more (equity investment less than $500,000)	$ 24	$ 37
Equity Securities
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	$ 1,987	$ 1,819
Number Of Securities Other Than Temporary Impairment Losses1 | security	0
Number Of Securities Continuous Unrealized Loss Position More Than Twelve Months	0	0
Unrealized losses 12 months or more (equity investment less than $500,000)	$ 0	$ 0
Procter And Gamble Company, Exxon Mobile Corporation And Chevron Corporation [Member]
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	$ 597
Common equities
Gain (Loss) on Investments [Line Items]
Number of securities	7