Condensed Financial Information of Parent Company - Balance Sheets (Parenthetical) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fixed Maturities, cost	$ 35,398	$ 34,762
Equity Securities, cost	1,244	1,264
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	110,217,445	99,519,509
Parent Company [Member]
Fixed Maturities, cost	1,273	935
Equity Securities, cost	$ 176	$ 200
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	110,217,445	99,519,509