Investments (Mortgage Loans by Portfolio Segment) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Company-held mortgage loans held-for-investment, net
Commercial mortgage loans	$ 49,549	$ 48,035
Percentage of loans receivable on commercial mortgage loans	63.90%	64.40%
Agricultural mortgage loans	$ 14,877	$ 14,456
Percentage of loans receivable on agricultural mortgage loans	19.20%	19.40%
Residential mortgage loans	$ 12,764	$ 11,696
Percentage of loans receivable on residential mortgage loans	16.40%	15.70%
Subtotal	$ 77,190	$ 74,187
Percentage of loans receivable on subtotal	99.50%	99.50%
Valuation allowances	$ (356)	$ (344)	$ (467)	$ (318)
Percentage of loans receivable on valuation allowances	(0.50%)	(0.50%)
Subtotal mortgage loans, net	$ 76,834	$ 73,843
Percentage of loans receivable on subtotal mortgage loans held-for-investment, net	99.00%	99.00%
Percentage of residential mortgage loans - FVO	0.80%	0.80%
Percentage of loans receivable on commercial mortgage loans held by consolidated securitization entities - fair value option	0.20%	0.20%
Total mortgage loans, net	$ 77,572	$ 74,545
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	$ 615	$ 566
Consolidated Securitization Entities
Company-held mortgage loans held-for-investment, net
Total mortgage loans, net	$ 123	$ 136