Investments (Valuation Allowance Rollforward by Portfolio Segment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance ALLL, Beginning of Period	$ 314	$ 304	$ 281
Provision for Loan and Lease Losses	36	24	183
Allowance for Loan and Lease Losses, Write-offs	8	14	160
Balance ALLL, Ending of Period	342	314	304
Commercial mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance ALLL, Beginning of Period	214	202	188
Provision for Loan and Lease Losses	24	12	157
Allowance for Loan and Lease Losses, Write-offs	0	0	143
Balance ALLL, Ending of Period	238	214	202
Agricultural Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance ALLL, Beginning of Period	41	39	37
Provision for Loan and Lease Losses	5	4	3
Allowance for Loan and Lease Losses, Write-offs	0	2	1
Balance ALLL, Ending of Period	46	41	39
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance ALLL, Beginning of Period	59	63	56
Provision for Loan and Lease Losses	7	8	23
Allowance for Loan and Lease Losses, Write-offs	8	12	16
Balance ALLL, Ending of Period	$ 58	$ 59	$ 63