Investments - Investments - Commercial Mortgage Loans Credit Quality (Details) $ in Millions	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Financing Receivable, Recorded Investment [Line Items]
Carrying Value	$ 3,637	$ 3,704
Commercial Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Carrying Value	$ 3,637	$ 3,704
Avg. Debt-Service Coverage Ratio	2.48	2.49
Commercial Loan [Member] | 65% - 80%
Financing Receivable, Recorded Investment [Line Items]
Carrying Value	$ 390	$ 386
Avg. Debt-Service Coverage Ratio	1.58	1.60
Commercial Loan [Member] | Less than 65%
Financing Receivable, Recorded Investment [Line Items]
Carrying Value	$ 3,247	$ 3,318
Avg. Debt-Service Coverage Ratio	2.58	2.59