Investments (Mortgage Loans by Portfolio Segment) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Company-held mortgage loans held-for-investment, net
Commercial mortgage loans	$ 48,035	$ 44,012
Percentage of loans receivable on commercial mortgage loans	64.40%	65.60%
Agricultural mortgage loans	$ 14,456	$ 13,188
Percentage of loans receivable on agricultural mortgage loans	19.40%	19.60%
Residential mortgage loans	$ 11,696	$ 9,734
Percentage of loans receivable on residential mortgage loans	15.70%	14.50%
Subtotal	$ 74,187	$ 66,934
Percentage of loans receivable on subtotal	99.50%	99.70%
Valuation allowances	$ (344)	$ (318)	$ (305)	$ (322)
Percentage of loans receivable on valuation allowances	0.50%	0.50%
Subtotal mortgage loans, net	$ 73,843	$ 66,616
Percentage of loans receivable on subtotal mortgage loans held-for-investment, net	99.00%	99.20%
Percentage of residential mortgage loans - FVO	0.80%	0.50%
Percentage of loans receivable on commercial mortgage loans held by consolidated securitization entities - fair value option	0.20%	0.30%
Total mortgage loans, net	$ 74,545	$ 67,102
Percentage of loans held for sale on total mortgage loans, net	100.00%	100.00%
Residential — FVO
Company-held mortgage loans held-for-investment, net
Total mortgage loans, net	$ 566	$ 314
Consolidated Securitization Entities
Company-held mortgage loans held-for-investment, net
Total mortgage loans, net	$ 136	$ 172