Investments - Additional Information (Detail) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2015 USD ($) security	Jun. 30, 2015 USD ($) security	Dec. 31, 2014 USD ($) security
Gain (Loss) on Investments [Line Items]
Short-term investments, at fair value (amortized cost: 2015—$75; 2014—$0)	$ 75	$ 75	$ 0
Largest equity holdings to total equity portfolio	3.90%	3.90%
Largest equity holdings to total portfolio	1.20%	1.20%
Unrealized losses 12 months or more (equity investment less than $500,000)	$ 10	$ 10	$ 11
Number Of Securities Other Than Temporary Impairment Losses			6
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	$ 493	$ 493	$ 607
Number Of Securities Other Than Temporary Impairment Losses1 | security	3
Number Of Securities Continuous Unrealized Loss Position More Than Twelve Months | security	71	71	144
Unrealized losses 12 months or more (equity investment less than $500,000)	$ 10	$ 10	$ 10
Equity Securities
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	$ 1,915	$ 1,915	$ 2,134
Number Of Securities Other Than Temporary Impairment Losses1 | security	2
Number Of Securities Continuous Unrealized Loss Position More Than Twelve Months	1	1	3
Unrealized losses 12 months or more (equity investment less than $500,000)	$ 0	$ 0	$ 1
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss, Accumulated in Investments	1	1	$ 1
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	$ 594	$ 594
Common equities
Gain (Loss) on Investments [Line Items]
Number of securities	7	7