Investment Income (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	$ 1,184	$ 1,183	$ 1,143
Less: investment expenses	40	37	38
Net investment income	1,144	1,146	1,105
Fixed Maturities [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	843	817	788
Equity securities [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	4	6	6
Commercial Mortgage Loans [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	192	218	221
Policy Loans [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	74	86	90
Real estate and mortgage loans, including pooled separate accounts [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	(2)	(2)	(2)
Other Long Term Investments [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	59	48	29
Short-term investments and cash [Member]
Schedule Of Investment Income Reported Amounts By Category [Line Items]
Gross investment income	$ 14	$ 10	$ 11