Investments (Past Due and Interest Accrual Status of Mortgage Loans) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past Due	$ 822	$ 501
Greater than 90 Days Past Due and Still Accruing Interest	135	2
Financing Receivable, Nonaccrual	992	681
Agricultural Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past Due	281	124
Greater than 90 Days Past Due and Still Accruing Interest	88	2
Financing Receivable, Nonaccrual	194	137	$ 105
Commercial Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past Due	0	0
Greater than 90 Days Past Due and Still Accruing Interest	0	0
Financing Receivable, Nonaccrual	302	167	167
Residential Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past Due	541	377
Greater than 90 Days Past Due and Still Accruing Interest	47	0
Financing Receivable, Nonaccrual	$ 496	$ 377	$ 402