Investments (Valuation Allowance Rollforward by Portfolio Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	$ 342	$ 314
Provision (release)	10	14
Charge-offs, net of recoveries	(2)	(1)
Balance, end of period	350	327
Agricultural Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	46	41
Provision (release)	1	0
Charge-offs, net of recoveries	0	0
Balance, end of period	47	41
Commercial Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	238	214
Provision (release)	7	14
Charge-offs, net of recoveries	0	0
Balance, end of period	245	228
Residential Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period	58	59
Provision (release)	2	0
Charge-offs, net of recoveries	(2)	(1)
Balance, end of period	$ 58	$ 58