Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands				1 Months Ended	5 Months Ended	12 Months Ended
	Oct. 29, 2015	Mar. 13, 2015	Nov. 10, 2014	Oct. 31, 2013	Mar. 13, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jul. 03, 2015	Nov. 07, 2014	Sep. 30, 2014
Equity, Class of Treasury Stock [Line Items]
Cash dividend declared						$ 1.15	$ 1.11	$ 1.07
Total Amount						$ 170,000,000	$ 170,000,000	$ 167,000,000
Value of shares repurchased						$ 385,000,000	$ 872,000,000	$ 531,000,000
Common shares acquired in connection with employee stock plans, shares						300	400	300
Common shares acquired in connection with employee stock plans, amount						$ 56,000,000	$ 42,000,000	$ 29,000,000
Aggregate statutory capital and surplus in our state regulated insurance subsidiaries						6,600,000,000	6,000,000,000
Aggregate minimum regulatory requirements of statutory capital and surplus						4,600,000,000	$ 4,100,000,000
Dividends that may be paid to the parent company without prior approval by state regulatory authorities in 2014						900,000,000
Dividends that were paid to the parent company without prior approval by state regulatory authorities						$ 493,000,000
Dividend Declared
Equity, Class of Treasury Stock [Line Items]
Cash dividend declared	$ 0.29
Dividend payable date				Jan. 29, 2016
Record Date				Dec. 30, 2015
Total Amount	$ 43,000,000
Prior Authorization
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization											$ 1,000,000,000
Remaining authorized amount											816,000,000
Current Authorization
Equity, Class of Treasury Stock [Line Items]
Expiration date of current authorization						Dec. 31, 2016
Share repurchase authorization											$ 2,000,000,000
Accelerated Share Repurchase Agreement
Equity, Class of Treasury Stock [Line Items]
ASR, settlement receipt, shares		360
ASR final price paid per share					$ 146.21
Share repurchase authorization										$ 500,000,000
Shares repurchased in open market			3,060		3,420
Value of shares repurchased			$ 400,000,000
Decrease in capital in excess of par value			$ 100,000,000
September 2014 Authorization
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization						$ 2,000,000,000
Shares repurchased in open market						1,850	4,100	0
Value of shares repurchased						$ 329,000,000	$ 635,000,000	$ 0
Remaining authorized amount									$ 1,040,000,000
April 2014 Authorization
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization						$ 1,000,000,000
Shares repurchased in open market						0	1,500	0
Value of shares repurchased						$ 0	$ 184,000,000	$ 0
April 2013 Authorization
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization						$ 1,000,000,000
Shares repurchased in open market						0	100	4,550
Value of shares repurchased						$ 0	$ 11,000,000	$ 420,000,000
April 2012 Authorization
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization						$ 1,000,000,000
Shares repurchased in open market						0	0	1,220
Value of shares repurchased						$ 0	$ 0	$ 82,000,000
Excluding Employee Stock Plans and ASR
Equity, Class of Treasury Stock [Line Items]
Shares repurchased in open market						1,850	5,700	5,770
Value of shares repurchased						$ 329,000,000	$ 830,000,000	$ 502,000,000