Investments (Narrative) (Details) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gain (Loss) on Securities [Line Items]
Non-income producing fixed maturity securities	$ 0	$ 2,000,000
Investments that exceed ten percent of stockholders' equity	0	0
Limited partnership investments	1,982,000,000	2,369,000,000
Undistributed earnings of limited partnership investments	$ 153,000,000	$ 539,000,000
Percentage of limited partnerships reported on a current basis	60.00%
Percentage of limited partnerships reported on a one month lag	14.00%
Percentage of limited partnerships employing hedge fund strategies focused on fixed income and equity investments	65.00%	71.00%
Limited partnerships invested in private debt and equity	30.00%	25.00%
Percentage of equity related limited partnership hedge fund strategies	60.00%
Percentage of multistrategy approach limited partnership hedge fund strategies	18.00%
Percentage of distressed investments limited partnership hedge fund strategies	19.00%
Percentage of fixed income limited partnership hedge fund strategies	3.00%
Carrying value of ten largest limited partnerships	$ 876,000,000	$ 1,136,000,000
Carrying value of limited partnerships as percentage of aggregate partnership equity	2.00%	3.00%
Income as percentage of change in partnership equity for all limited partnerships	3.00%	3.00%	4.00%
Obligation to return cash	$ 0	$ 0
RIght to reclaim cash	0	0
Derivative, notional amount	172,000,000	167,000,000
Derivative asset	4,000,000
Derivative liability, fair value, gross liability		(3,000,000)
Future capital call commitments for limited partnership investments	574,000,000
Mortgage loan commitments	59,000,000
Commitments to purchase or fund privately placed debt securities	230,000,000
Commitments to sell various privately placed debt securities	78,000,000
Carrying value of securities deposited under requirements of regulatory authorities	2,500,000,000	2,600,000,000
Cash and securities deposited as collateral for letters of credit	1,000,000,000	1,100,000,000
Senior notes of CNAF, 6.950%, face amount of $150, due November, 2019 \| Senior Notes
Gain (Loss) on Securities [Line Items]
Realized investment gains (losses)		(42,000,000)
Face amount		$ 350,000,000
Common Stock
Gain (Loss) on Securities [Line Items]
Equity securities, FV-NI, gain (loss)	24,000,000
Preferred stock
Gain (Loss) on Securities [Line Items]
Equity securities, FV-NI, gain (loss)	$ 73,000,000

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