Condensed Consolidated Statements of Equity (Unaudited) (USD $) In Millions	Total	Common stock [Member]	Additional paid-in capital [Member]	Retained earnings [Member]	Accumulated other comprehensive income (loss) [Member]	Treasury stock [Member]	Notes receivable for the issuance of common stock [Member]	Stockholder's Equity [Member]	Noncontrolling interest [Member]
Balance at Dec. 31, 2010		$ 683	$ 2,200	$ 7,876	$ 326	$ (105)	$ (26)		$ 570
Cumulative effect adjustment from accounting change for deferred acquisition costs, net of tax (Accounting standards update 2010-26 [Member])				(72)					(7)
Dividends paid to common stockholders				(81)
Net income (loss)	434			419					15
Other comprehensive income (loss)	558				550				8
Stock-based compensation			3			3
(Increase) decrease in notes receivable from the issuance of common stock							4
Acquisition of CNA Surety noncontrolling interest			(65)		19				(429)
Other			1						(12)
Balance at Sep. 30, 2011	11,880	683	2,139	8,142	895	(102)	(22)	11,735	145
Balance at Dec. 31, 2011		683	2,146	8,382	470	(102)	(22)
Cumulative effect adjustment from accounting change for deferred acquisition costs, net of tax (Accounting standards update 2010-26 [Member])			(5)	(74)	10
Dividends paid to common stockholders				(122)
Net income (loss)	637			637
Other comprehensive income (loss)	650				650
Stock-based compensation			3			3
(Increase) decrease in notes receivable from the issuance of common stock							1
Acquisition of CNA Surety noncontrolling interest
Other
Balance at Sep. 30, 2012	$ 12,660	$ 683	$ 2,144	$ 8,823	$ 1,130	$ (99)	$ (21)	$ 12,660