Investments (Analysis of Past Due Commercial Mortgage and Other Loans) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Current	$ 63,764	$ 63,663
Total Past Due	35	17
Total Loans	63,799	63,680
Non-Accrual Status	62	59
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	13	2
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	8	0
90 days or more past due
Financing Receivable, Past Due [Line Items]
Total Past Due	14	15
Commercial Mortgage Loans
Financing Receivable, Past Due [Line Items]
Current	59,157	59,363
Total Past Due	10	0
Total Loans	59,167	59,363
Non-Accrual Status	44	44
Commercial Mortgage Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	2	0
Commercial Mortgage Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	8	0
Commercial Mortgage Loans | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Agricultural property loans
Financing Receivable, Past Due [Line Items]
Current	3,642	3,458
Total Past Due	23	14
Total Loans	3,665	3,472
Non-Accrual Status	13	13
Agricultural property loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	10	1
Agricultural property loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Agricultural property loans | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total Past Due	13	13
Residential Property Loans
Financing Receivable, Past Due [Line Items]
Current	113	121
Total Past Due	2	3
Total Loans	115	124
Non-Accrual Status	1	2
Residential Property Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	1	1
Residential Property Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Residential Property Loans | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total Past Due	1	2
Other Collateralized Loans
Financing Receivable, Past Due [Line Items]
Current	192	65
Total Past Due	0	0
Total Loans	192	65
Non-Accrual Status	0	0
Other Collateralized Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Other Collateralized Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Other Collateralized Loans | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Uncollateralized loans
Financing Receivable, Past Due [Line Items]
Current	660	656
Total Past Due	0	0
Total Loans	660	656
Non-Accrual Status	4	0
Uncollateralized loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Uncollateralized loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Uncollateralized loans | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Loans | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Accruing Interest	$ 0	$ 0