Stockholders' Equity - Additional Information (Detail) - USD ($)			3 Months Ended						5 Months Ended
	Mar. 13, 2015	Nov. 10, 2014	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Mar. 13, 2015	Jul. 03, 2015	Aug. 31, 2014
Equity, Class of Treasury Stock [Line Items]
Cash dividend per share			$ 0.29	$ 0.29	$ 0.29	$ 0.29	$ 0.28	$ 0.28
Share repurchase authorization											$ 1,000,000,000
Remaining authorized amount											$ 816,000,000
Common shares acquired in connection with employee stock plans, shares			430,000				250,000
Common shares acquired in connection with employee stock plans, amount			$ 71,000,000				$ 40,000,000
Treasury stock reissued (shares)			1,150,000
Treasury stock reissued			$ 76,000,000
Accumulated other comprehensive income			76,000,000	$ 58,000,000
Net unrealized gains on our investment securities
Equity, Class of Treasury Stock [Line Items]
Accumulated other comprehensive income			144,000,000	58,000,000
Additional liability that would exist on closed block of long-term care policies assuming unrealized gains on investments backing such products were realized and reinvested at current yields
Equity, Class of Treasury Stock [Line Items]
Accumulated other comprehensive income			$ 68,000,000	$ 0
September 2014 Share Repurchase Authorization
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization							2,000,000,000
Remaining authorized amount										$ 1,040,000,000
Expiration date of new authorization			Dec. 31, 2016
Value of shares repurchased							$ 26,000,000
Shares repurchased in open market			0				150,000
Accelerated Share Repurchase Agreement
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization		$ 500,000,000
Value of shares repurchased		$ 400,000,000							$ 500,000,000
Shares repurchased in open market		3,060,000							3,420,000
Decrease in capital in excess of par value		$ 100,000,000
ASR, shares received	360,000
Shares repurchased in open market, average price									$ 146.21