Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands			3 Months Ended							5 Months Ended	6 Months Ended
	Mar. 13, 2015	Nov. 10, 2014	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Mar. 13, 2015	Jun. 30, 2015	Jun. 30, 2014	Jul. 03, 2015	Nov. 07, 2014	Aug. 31, 2014	Apr. 30, 2014	Apr. 30, 2013
Equity, Class of Treasury Stock [Line Items]
Cash dividend per share			$ 0.29	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.27	$ 0.27
Payment Date			Jul. 31, 2015	Apr. 24, 2015	Jan. 30, 2015	Oct. 31, 2014	Jul. 25, 2014	Apr. 25, 2014	Jan. 31, 2014
Record Date			Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Share repurchase authorization															$ 1,000,000,000
Remaining authorized amount															$ 816,000,000
Value of shares repurchased											$ 329,000,000	$ 112,000,000
Shares repurchased in open market											1,850	910
Common shares acquired in connection with employee stock plans, shares											300	400
Common shares acquired in connection with employee stock plans, amount											$ 42,000,000	$ 40,000,000
Treasury stock reissued (shares)											700
Treasury stock reissued											$ 40,000,000
Accumulated other comprehensive income			$ 153,000,000		$ 223,000,000						153,000,000
Net unrealized gains on our investment securities
Equity, Class of Treasury Stock [Line Items]
Accumulated other comprehensive income			162,000,000		301,000,000						162,000,000
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			$ 9,000,000		$ 78,000,000						$ 9,000,000
September 2014 Share Repurchase Authorization
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization						$ 2,000,000,000
Expiration date of new authorization											Dec. 31, 2016
Value of shares repurchased											$ 329,000,000	$ 0
Shares repurchased in open market											1,850	0
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								3,420
Decrease in capital in excess of par value		$ 100,000,000
ASR, shares received	360
Shares repurchased in open market, average price										$ 146.21
April 2014 Share Repurchase Authorization
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization																$ 1,000,000,000
Value of shares repurchased											$ 0	$ 101,000,000
Shares repurchased in open market											0	810
April 2013 Share Repurchase Authorization
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization																	$ 1,000,000,000
Value of shares repurchased											$ 0	$ 11,000,000
Shares repurchased in open market											0	100
Subsequent Event | September 2014 Share Repurchase Authorization
Equity, Class of Treasury Stock [Line Items]
Remaining authorized amount													$ 1,040,000,000