Investments (Past Due Mortgage Loans by Portfolio Segment) (Details) - Mortgage Loans - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, current	$ 15,583
Financing receivable, before allowance for credit losses	15,749	$ 15,728
30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	65
60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	69
90 to 179 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	17
180 Days and Greater Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	15
Commercial
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, current	9,803
Financing receivable, before allowance for credit losses	9,803	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	3,319
Financing receivable, before allowance for credit losses	3,320	3,326
Agricultural | 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	0
Agricultural | 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	0
Agricultural | 90 to 179 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	1
Agricultural | 180 Days and Greater Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	0
Residential
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, current	2,461
Financing receivable, before allowance for credit losses	2,626	$ 2,708
Residential | 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	65
Residential | 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	69
Residential | 90 to 179 Days Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	16
Residential | 180 Days and Greater Past Due
Financing Receivable, Past Due [Line Items]
Financing receivable before allowance for credit losses, past due	$ 15