Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Gain (Loss) on Investments [Line Items]
Short-term investments, at fair value (amortized cost: 2015—$25; 2014—$0)	$ 25	$ 0
Largest equity holdings to total equity portfolio	3.80%
Largest equity holdings to total portfolio	1.20%
Unrealized losses 12 months or more (equity investment less than $500,000)	5	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	648	607
Number Of Securities Other Than Temporary Impairment Losses1	0
Number Of Securities Continuous Unrealized Loss Position More Than Twelve Months	70	144
Unrealized losses 12 months or more (equity investment less than $500,000)	5	10
Equity Securities
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	2,052	2,134
Number Of Securities Other Than Temporary Impairment Losses1	0
Number Of Securities Continuous Unrealized Loss Position More Than Twelve Months	2	3
Unrealized losses 12 months or more (equity investment less than $500,000)	0	1
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss, Accumulated in Investments		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	$ 605
Common equities
Gain (Loss) on Investments [Line Items]
Number of securities	7