Investments (Valuation Allowance Rollforward by Portfolio Segment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance ALLL, Beginning of Period	$ 342	$ 314	$ 304
Provision (release)	26	36	24
Charge-offs, net of recoveries	(15)	(8)	(14)
Balance ALLL, Ending of Period	353	342	314
Commercial Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance ALLL, Beginning of Period	238	214	202
Provision (release)	8	24	12
Charge-offs, net of recoveries	0	0	0
Balance ALLL, Ending of Period	246	238	214
Residential Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance ALLL, Beginning of Period	58	59	63
Provision (release)	7	7	8
Charge-offs, net of recoveries	(10)	(8)	(12)
Balance ALLL, Ending of Period	55	58	59
Agricultural Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance ALLL, Beginning of Period	46	41	39
Provision (release)	11	5	4
Charge-offs, net of recoveries	(5)	0	(2)
Balance ALLL, Ending of Period	$ 52	$ 46	$ 41