Schedule I-Parent Company Financial Information (Notes to Condensed Financial Statements) - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Cash dividends received from subsidiaries	$ 927,000,000	$ 967,000,000	$ 1,200,000,000
Interest-bearing rate minimum	0.98%
Interest-bearing rate maximum	6.65%
Aggregate statutory capital and surplus in our state regulated insurance subsidiaries	6,000,000,000	5,500,000,000
Aggregate minimum regulatory requirements of statutory capital and surplus	4,100,000,000	3,500,000,000
Dividends that may be paid to the parent company without prior approval by state regulatory authorities in 2014	800,000,000
Dividends that were paid to the parent company without prior approval by state regulatory authorities	927,000,000
Majority-Owned Subsidiary, Unconsolidated
Condensed Financial Statements, Captions [Line Items]
Interest expense on subsidiary notes payable	$ 1,000,000	$ 1,000,000	$ 1,000,000