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				(54)
Net income (loss)	358			344					14
Other comprehensive income (loss)	393				385				8
Stock-based compensation			1			3
(Increase) decrease in notes receivable from the issuance of common stock							3
Acquisition of CNA Surety noncontrolling interest			(65)		19				(429)
Other			2						(12)
Balance at Jun. 30, 2011	11,664	683	2,138	8,094	730	(102)	(23)	11,520	144
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				(81)
Net income (loss)	416			416
Other comprehensive income (loss)	387				387
Stock-based compensation						3
(Increase) decrease in notes receivable from the issuance of common stock							1
Acquisition of CNA Surety noncontrolling interest
Other
Balance at Jun. 30, 2012	$ 12,214	$ 683	$ 2,141	$ 8,643	$ 867	$ (99)	$ (21)	$ 12,214