Investments (Past Due Mortgage Loans by Portfolio Segment) (Details) - Mortgage Loans - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, current	$ 15,454
Financing receivable, before allowance for credit losses	15,525	$ 15,728
30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	7
60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	16
90 to 179 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	13
180 Days and Greater Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	35
Commercial
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, current	9,484
Financing receivable, before allowance for credit losses	9,484	9,694
Commercial | 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	0
Commercial | 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	0
Commercial | 90 to 179 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	0
Commercial | 180 Days and Greater Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	0
Agricultural
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, current	3,311
Financing receivable, before allowance for credit losses	3,340	3,326
Agricultural | 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	5
Agricultural | 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	3
Agricultural | 90 to 179 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	0
Agricultural | 180 Days and Greater Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	21
Residential
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, current	2,659
Financing receivable, before allowance for credit losses	2,701	$ 2,708
Residential | 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	2
Residential | 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	13
Residential | 90 to 179 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	13
Residential | 180 Days and Greater Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	$ 14