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, 2014	Dec. 31, 2013	Dec. 31, 2012
Combined Continental Casualty Companies [Member]
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	$ 11,155	$ 11,137
Statutory net income (loss)	914	913	391
Life Company [Member]
Statutory Accounting Practices [Line Items]
Statutory capital and surplus		597
Statutory net income (loss)	$ 37	$ 48	$ 44