Investments (Past Due and Interest Accrual Status of Mortgage Loans) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Nonaccrual [Line Items]
Mortgage Loans, Gross	$ 84,344	$ 80,635
Greater than 90 Days Past Due and Still Accruing Interest	91	51
Nonaccrual	1,117	731
Financing Receivables , Past Due
Financing Receivable, Nonaccrual [Line Items]
Mortgage Loans, Gross	818	591
Commercial Mortgage Loans
Financing Receivable, Nonaccrual [Line Items]
Mortgage Loans, Gross	52,434	49,624
Greater than 90 Days Past Due and Still Accruing Interest	7	9
Nonaccrual	317	176	$ 176
Commercial Mortgage Loans | Financing Receivables , Past Due
Financing Receivable, Nonaccrual [Line Items]
Mortgage Loans, Gross	10	10
Residential Mortgage Loans
Financing Receivable, Nonaccrual [Line Items]
Mortgage Loans, Gross	13,782	14,316
Greater than 90 Days Past Due and Still Accruing Interest	64	35
Nonaccrual	534	418	436
Residential Mortgage Loans | Financing Receivables , Past Due
Financing Receivable, Nonaccrual [Line Items]
Mortgage Loans, Gross	556	452
Agricultural Mortgage Loans
Financing Receivable, Nonaccrual [Line Items]
Mortgage Loans, Gross	18,128	16,695
Greater than 90 Days Past Due and Still Accruing Interest	20	7
Nonaccrual	266	137	$ 105
Agricultural Mortgage Loans | Financing Receivables , Past Due
Financing Receivable, Nonaccrual [Line Items]
Mortgage Loans, Gross	$ 252	$ 129