Fair Values of Financial Instruments - Carrying Values and Fair Values of Financial Instruments (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short Term Investments	$ 1,411	$ 1,318
Fixed maturities	37,880	38,780
Equity securities	1,957	1,964
Long Term Debt	3,300	3,300
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short Term Investments	1,411	1,318
Fixed maturities	37,880	38,780
Equity securities	1,957	1,964
Long Term Debt	3,300	3,300
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short Term Investments	1,411	1,318
Fixed maturities	37,880	38,780
Equity securities	1,957	1,964
Long Term Debt	$ 3,864	$ 4,013