Investments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net unrealized gains (losses) related to changes in fair value of trading securities still held included in net investment income
Number of non-income producing fixed maturity securities	9	9
Fair value of non income fixed maturity security	1	3
Number of investments that exceed ten percent of stockholders' equity
Net unrealized gains (losses) related to changes in the fair value of securities for which the fair value option has been elected	(1)	2	(1)
Limited partnership investments	2,462	2,245
Undistributed earnings of limited partnership investments	768	560
Percentage of limited partnerships reported on a current basis	67.00%
Percentage of limited partnerships reported on a one month lag	17.00%
Number of active limited partnership investments held	79	79
Percentage of limited partnerships employing hedge fund strategies focused on fixed income and equity investments	80.00%	81.00%
Percentage of equity related limited partnership hedge fund strategies	48.00%
Percentage of multistrategy approach limited partnership hedge fund strategies	27.00%
Percentage of distressed investments limited partnership hedge fund strategies	22.00%
Percentage of fixed income limited partnership hedge fund strategies	3.00%
Limited partnerships invested in private equity	16.00%	14.00%
Carrying value of ten largest limited partnerships	1,309	1,218
Carrying value of limited partnerships as percentage of aggregate partnership equity	4.00%	4.00%
Income As Percentage Of Change In Partnership Equity For All Limited Partnerships	3.00%	4.00%	3.00%
Commercial mortgage loans past due or in non-accrual status
Valuation allowances recorded on commercial mortgage loans
Future capital call commitments for limited partnership investments	202
Mortgage loan commitments	22
Commitments to purchase various privately placed debt securities	185
Commitments to sell various privately placed debt securities	164
Carrying value of securities deposited under requirements of regulatory authorities	3,600	3,500
Cash and securities deposited as collateral for letters of credit	4	5
Carrying value of assets deposited to secure reinsurance and third party obligations	$ 277	$ 288