Investments (Mortgage Loans by Portfolio Segment) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Carrying value	$ 15,728	$ 13,652
Mortgage loans, gross as a percentage of total mortgage loans, net	100.40%	100.40%
Mortgage loans valuation allowances	$ (64)	$ (56)
Mortgage loans valuation allowances as a percentage of total mortgage loans, net	(0.40%)	(0.40%)
Mortgage loans, net	$ 15,664	$ 13,596
Mortgage loans, net as a percentage of total mortgage loans, net	100.00%	100.00%
Mortgage Loans | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Carrying value	$ 9,694	$ 8,502
Mortgage loans, gross as a percentage of total mortgage loans, net	61.90%	62.60%
Mortgage Loans | Agricultural
Loans and Leases Receivable Disclosure [Line Items]
Carrying value	$ 3,326	$ 2,874
Mortgage loans, gross as a percentage of total mortgage loans, net	21.20%	21.10%
Mortgage Loans | Residential
Loans and Leases Receivable Disclosure [Line Items]
Carrying value	$ 2,708	$ 2,276
Mortgage loans, gross as a percentage of total mortgage loans, net	17.30%	16.70%