Investments (Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of year	$ 121	$ 128
Cumulative effect of adoption of ASU 2016-13	115
Addition to (release of) allowance for credit losses	1	(6)
Charge-offs, net of recoveries		(1)
Change in foreign exchange		0
Other	3
Total ending balance	240	121
Commercial Mortgage Loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of year	114	120
Cumulative effect of adoption of ASU 2016-13	110
Addition to (release of) allowance for credit losses	1	(5)
Charge-offs, net of recoveries		(1)
Change in foreign exchange		0
Other	0
Total ending balance	225	114
Agricultural Property Loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of year	3	3
Cumulative effect of adoption of ASU 2016-13	5
Addition to (release of) allowance for credit losses	0	0
Charge-offs, net of recoveries		0
Change in foreign exchange		0
Other	0
Total ending balance	8	3
Residential Property Loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of year	0	0
Cumulative effect of adoption of ASU 2016-13	0
Addition to (release of) allowance for credit losses	0	0
Charge-offs, net of recoveries		0
Change in foreign exchange		0
Other	0
Total ending balance	0	0
Other Collateralized Loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of year	0	0
Cumulative effect of adoption of ASU 2016-13	0
Addition to (release of) allowance for credit losses	0	0
Charge-offs, net of recoveries		0
Change in foreign exchange		0
Other	3
Total ending balance	3	0
Uncollateralized Loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of year	4	5
Cumulative effect of adoption of ASU 2016-13	0
Addition to (release of) allowance for credit losses	0	(1)
Charge-offs, net of recoveries		0
Change in foreign exchange		0
Other	0
Total ending balance	$ 4	$ 4