Investments (Valuation Allowance Rollforward by Portfolio Segment) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	$ 342	$ 314
Provision (release)	19	15
Charge-offs, net of recoveries	(4)	(4)
Balance, end of period	357	325
Agricultural Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	46	41
Provision (release)	2	0
Charge-offs, net of recoveries	0	0
Balance, end of period	48	41
Commercial Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	238	214
Provision (release)	8	13
Charge-offs, net of recoveries	0	0
Balance, end of period	246	227
Residential Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	58	59
Provision (release)	9	2
Charge-offs, net of recoveries	(4)	(4)
Balance, end of period	$ 63	$ 57