Stockholders' Equity - Additional Information (Detail) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended											1 Months Ended	9 Months Ended		1 Months Ended	9 Months Ended	1 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013 Net unrealized gains on our investment securities	Dec. 31, 2012 Net unrealized gains on our investment securities	Dec. 31, 2012 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, 2013 Prior Authorization	Sep. 30, 2013 Prior Authorization	Sep. 30, 2012 Prior Authorization	Apr. 30, 2012 Current Authorization	Sep. 30, 2013 Current Authorization	Oct. 31, 2013 Subsequent Event Dividend Declared	Nov. 06, 2013 Subsequent Event Current Authorization
Equity, Class of Treasury Stock [Line Items]
Cash dividend declared	$ 0.27	$ 0.26	$ 0.80				$ 0.77												$ 0.27
Dividend payable date			Oct. 25, 2013	Jul. 26, 2013	Apr. 26, 2013	Jan. 25, 2013	Oct. 26, 2012	Jul. 27, 2012	Apr. 27, 2012	Jan. 31, 2012									Jan. 31, 2014
Record Date			Sep. 30, 2013	Jun. 28, 2013	Mar. 28, 2013	Dec. 31, 2012	Sep. 28, 2012	Jun. 29, 2012	Mar. 30, 2012	Dec. 30, 2011									Dec. 31, 2013
Expiration date of current authorization																		Jun. 30, 2015
Share repurchase authorization														$ 1,000,000,000			$ 1,000,000,000
Share repurchase authorization														In April 2013, the Board of Directors replaced its previously approved share repurchase authorization of up to $1 billion (of which $557 million remained unused) with the current 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, 2015.
Shares repurchased in open market															1.22	6.25		2.56
Value of shares repurchased															82,000,000	460,000,000		219,000,000
Shares repurchased in open market, average price															$ 67.59	$ 73.66		$ 85.63
Remaining authorized amount														557,000,000						781,000,000
Common shares acquired in connection with employee stock plans, shares			0.3				0.6
Common shares acquired in connection with employee stock plans, amount			24,000,000				53,000,000
Accumulated other comprehensive income	$ 196,000,000		$ 196,000,000			$ 386,000,000					$ 196,000,000	$ 462,000,000	$ 76,000,000