Stockholders' Equity - Additional Information (Detail) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended						12 Months Ended			1 Months Ended		12 Months Ended			1 Months Ended	12 Months Ended	1 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Oct. 31, 2012 Dividend Declared	Apr. 30, 2012 Prior Authorization	Dec. 31, 2012 Prior Authorization	Dec. 31, 2011 Prior Authorization	Dec. 31, 2010 Prior Authorization	Apr. 30, 2012 $1 Billion Authorization	Dec. 31, 2012 $1 Billion Authorization	Feb. 01, 2013 $1 Billion Authorization Subsequent Event
Equity, Class of Treasury Stock [Line Items]
Cash dividend declared							$ 1.03	$ 0.75	$ 0.00	$ 0.26
Total Amount	$ 41,000,000	$ 42,000,000	$ 41,000,000	$ 41,000,000	$ 41,000,000	$ 41,000,000				$ 42,000,000
Dividend payable date	Oct. 26, 2012	Jul. 27, 2012	Apr. 27, 2012	Jan. 31, 2012	Oct. 28, 2011	Jul. 28, 2011				Jan. 25, 2013
Record Date	Sep. 28, 2012	Jun. 29, 2012	Mar. 30, 2012	Dec. 30, 2011	Sep. 30, 2011	Jun. 30, 2011				Dec. 31, 2012
Expiration Date of April 2012 Authorization																Jun. 30, 2014
Share repurchase authorization											1,000,000,000				1,000,000,000
Share repurchase authorization											In April 2012, the Board of Directors replaced its previously approved share repurchase authorization of up to $1 billion (of which $461 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, 2014.
Shares repurchased in open market												1.15	6.80	1.99		5.10
Value of shares repurchased							518,000,000	541,000,000	108,000,000			100,000,000	492,000,000	100,000,000		360,000,000
Shares repurchased in open market, average price												$ 86.95	$ 72.75	$ 50.17		$ 70.66
Remaining authorized amount											461,000,000						640,000,000
Common shares acquired in connection with employee stock plans, shares							0.7	0.8	0.2
Common shares acquired in connection with employee stock plans, amount							58,000,000	49,000,000	8,000,000
Aggregate statutory capital and surplus in our state regulated subsidiaries				4,700,000,000			5,100,000,000	4,700,000,000
Dividends that were paid to the parent company without prior approval by state regulatory authorities							860,000,000
Dividends that may be paid to the parent company without prior approval by state regulatory authorities in 2013							$ 911,000,000