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	$ 40,262	$ 40,472
% of Total	100.00%	100.00%
Estimated Fair Value	42,031	43,082
% of Total	100.00%	100.00%
Less than 65% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	31,489	31,291
% of Total	78.20%	77.30%
Estimated Fair Value	33,188	33,730
% of Total	79.00%	78.30%
65% to 75% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	6,729	5,882
% of Total	16.70%	14.60%
Estimated Fair Value	6,860	6,129
% of Total	16.30%	14.20%
76% to 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	740	1,385
% of Total	1.80%	3.40%
Estimated Fair Value	737	1,436
% of Total	1.70%	3.30%
Greater than 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	1,304	1,914
% of Total	3.30%	4.70%
Estimated Fair Value	1,246	1,787
% of Total	3.00%	4.20%
Greater than 1.20x [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	37,213	36,919
Greater than 1.20x [Member] | Less than 65% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	29,992	29,839
Greater than 1.20x [Member] | 65% to 75% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	6,029	5,057
Greater than 1.20x [Member] | 76% to 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	290	938
Greater than 1.20x [Member] | Greater than 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	902	1,085
1.00x - 1.20x [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	1,705	2,085
1.00x - 1.20x [Member] | Less than 65% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	751	730
1.00x - 1.20x [Member] | 65% to 75% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	501	672
1.00x - 1.20x [Member] | 76% to 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	192	131
1.00x - 1.20x [Member] | Greater than 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	261	552
Less than 1.00x [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	1,344	1,468
Less than 1.00x [Member] | Less than 65% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	746	722
Less than 1.00x [Member] | 65% to 75% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	199	153
Less than 1.00x [Member] | 76% to 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	258	316
Less than 1.00x [Member] | Greater than 80% [Member]
Mortgage Loans on Real Estate [Line Items]
Commercial mortgage loans	$ 141	$ 277