Investments (Credit Quality of Commercial Mortgage Loans) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	$ 5,114	$ 5,266
% of Total	100.00%	100.00%
Estimated Fair Value	5,389	5,679
% of Total	100.00%	100.00%
Less than 65% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	4,067	4,083
% of Total	79.50%	77.50%
Estimated Fair Value	4,337	4,459
% of Total	80.50%	78.50%
65% to 75% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	935	685
% of Total	18.30%	13.00%
Estimated Fair Value	951	711
% of Total	17.60%	12.50%
76% to 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	25	408
% of Total	0.50%	7.80%
Estimated Fair Value	25	428
% of Total	0.50%	7.60%
Greater than 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	87	90
% of Total	1.70%	1.70%
Estimated Fair Value	76	81
% of Total	1.40%	1.40%
Greater than 1.20x [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	4,818	4,896
Greater than 1.20x [Member] | Less than 65% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	3,868	3,888
Greater than 1.20x [Member] | 65% to 75% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	898	626
Greater than 1.20x [Member] | 76% to 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	13	343
Greater than 1.20x [Member] | Greater than 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	39	39
1.00x - 1.20x [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	190	174
1.00x - 1.20x [Member] | Less than 65% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	142	106
1.00x - 1.20x [Member] | 65% to 75% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	10	32
1.00x - 1.20x [Member] | 76% to 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	12	8
1.00x - 1.20x [Member] | Greater than 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	26	28
Less than 1.00x [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	106	196
Less than 1.00x [Member] | Less than 65% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	57	89
Less than 1.00x [Member] | 65% to 75% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	27	27
Less than 1.00x [Member] | 76% to 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	0	57
Less than 1.00x [Member] | Greater than 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	$ 22	$ 23