Condensed Financial Information of Parent Company - Balance Sheets (Parenthetical) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Fixed Maturities, cost	$ 36,958	$ 35,959
Equity Securities, cost	1,089	1,057
Preferred Stock, Shares Authorized	8,000,000	8,000,000
Preferred Stock, Par Value	$ 1	$ 1
Preferred Stock, Shares Issued	0	0
Common Stock, Shares Authorized	1,200,000,000	1,200,000,000
Common Stock, Par Value	$ 1	$ 1
Common Stock, Shares Issued	371,980,460	371,980,460
Treasury Stock, Shares	139,551,071	123,673,969	110,217,445	99,519,509
Parent Company [Member]
Fixed Maturities, cost	1,213	1,095
Equity Securities, cost
Preferred Stock, Shares Authorized	8,000,000	8,000,000
Preferred Stock, Par Value	$ 1	$ 1
Preferred Stock, Shares Issued	0	0
Common Stock, Shares Authorized	1,200,000,000	1,200,000,000
Common Stock, Par Value	$ 1	$ 1
Common Stock, Shares Issued	371,980,460	371,980,460
Treasury Stock, Shares	139,551,071	123,673,969