Investments (Allowance for Credit Loss Rollforward by Portfolio Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	$ 353	$ 342
Adoption of new credit loss guidance	78	0
Provision (release)	36	10
Charge-offs, net of recoveries	(3)	(2)
Balance, end of period	464	350
Commercial Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	246	238
Adoption of new credit loss guidance	(118)	0
Provision (release)	15	7
Charge-offs, net of recoveries	0	0
Balance, end of period	143	245
Residential Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	55	58
Adoption of new credit loss guidance	161	0
Provision (release)	24	2
Charge-offs, net of recoveries	(3)	(2)
Balance, end of period	237	58
Agricultural Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	52	46
Adoption of new credit loss guidance	35	0
Provision (release)	(3)	1
Charge-offs, net of recoveries	0	0
Balance, end of period	$ 84	$ 47