Schedule I-Parent Company Financial Information (Notes to Condensed Financial Statements) - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Cash dividends received from subsidiary	$ 493	$ 927	$ 967
Interest-bearing rate minimum	1.51%
Interest-bearing rate maximum	6.65%
Aggregate statutory capital and surplus in our state regulated insurance subsidiaries	$ 6,600	6,000
Aggregate minimum regulatory requirements of statutory capital and surplus	4,600	4,100
Expected contributions of statutory capital and surplus into regulated subsidiaries (in first quarter of 2016)	450
Dividends that may be paid to the parent company without prior approval by state regulatory authorities in 2014	900
Dividends that were paid to the parent company without prior approval by state regulatory authorities	493
Majority-Owned Subsidiary, Unconsolidated
Condensed Financial Statements, Captions [Line Items]
Interest expense on subsidiary notes payable	1	$ 1	$ 1
Other long-term assets
Condensed Financial Statements, Captions [Line Items]
Related party receivable	$ 284