Stockholders' Equity - Additional Information (Detail) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended										1 Months Ended	3 Months Ended		1 Months Ended	3 Months Ended	0 Months Ended	1 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2014 Net unrealized gains on our investment securities	Dec. 31, 2013 Net unrealized gains on our investment securities	Mar. 31, 2014 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	Dec. 31, 2013 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	Apr. 30, 2014 Subsequent Event Dividend Declared	Mar. 31, 2014 Prior Authorization	Mar. 31, 2013 Prior Authorization	Apr. 30, 2014 Prior Authorization Subsequent Event	Mar. 31, 2014 New Authorization	May 07, 2014 New Authorization Subsequent Event	Apr. 30, 2014 New Authorization Subsequent Event
Equity, Class of Treasury Stock [Line Items]
Cash dividend declared	$ 0.27				$ 0.26						$ 0.28
Dividend payable date	Apr. 25, 2014	Jan. 31, 2014	Oct. 25, 2013	Jul. 26, 2013	Apr. 26, 2013	Jan. 25, 2013					Jul. 25, 2014
Record Date	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 28, 2013	Mar. 28, 2013	Dec. 31, 2012					Jun. 30, 2014
Expiration date of new authorization															Jun. 30, 2016
Share repurchase authorization														$ 1,000,000,000			$ 1,000,000,000
Share repurchase authorization														In April 2014, the Board of Directors replaced a previous share repurchase authorization of up to $1 billion (of which $569 million remained unused) with a new authorization for repurchases of up to $1 billion of our common shares exclusive of shares repurchased in connection with employee stock plans, expiring on June 30, 2016.
Shares repurchased in open market												0.10	1.21
Value of shares repurchased												11,000,000	81,000,000
Shares repurchased in open market, average price												$ 113.44	$ 67.60
Remaining authorized amount														569,000,000		1,000,000,000
Common shares acquired in connection with employee stock plans, shares	0.4				0.2
Common shares acquired in connection with employee stock plans, amount	38,000,000				13,000,000
Accumulated other comprehensive income	$ 226,000,000	$ 158,000,000					$ 238,000,000	$ 158,000,000	$ 12,000,000	$ 0