Stockholders' Equity and Statutory Accounting Practices Combined statutory capital and surplus and net income (loss) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Combined Continental Casualty Companies [Member]
Statutory capital and surplus	$ 10,026	[1],[2]	$ 9,888	[1]
Statutory net income (loss)	391	[1],[2]	954	[1]	258	[1]
Life Company [Member]
Statutory capital and surplus	556	[2]	519
Statutory net income (loss)	$ 44	[2]	$ 29		$ 86

[1] Represents the combined statutory surplus of CCC and its subsidiaries, including the life company.

[2] Information derived from the statutory-basis financial statements to be filed with insurance regulators.