Investments (Past Due and Interest Accrual Status of Mortgage Loans) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past Due	$ 684	$ 591
Greater than 90 Days Past Due and Still Accruing	137	51
Financing Receivable, Nonaccrual	739	731
Commercial Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past Due	6	10
Greater than 90 Days Past Due and Still Accruing	0	9
Financing Receivable, Nonaccrual	182	176	$ 176
Residential Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past Due	407	452
Greater than 90 Days Past Due and Still Accruing	16	35
Financing Receivable, Nonaccrual	391	418	436
Agricultural Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past Due	271	129
Greater than 90 Days Past Due and Still Accruing	121	7
Financing Receivable, Nonaccrual	$ 166	$ 137	$ 105