Investments - Mortgages by Year of Origination (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Total commercial mortgage loans	$ 4,812	$ 4,919
Year of Origination 2019
Investment [Line Items]
Total commercial mortgage loans	97	0
Year of Origination 2018
Investment [Line Items]
Total commercial mortgage loans	377	375
Year of Origination 2017
Investment [Line Items]
Total commercial mortgage loans	1,066	1,108
Year of Origination 2016
Investment [Line Items]
Total commercial mortgage loans	849	906
Year of Origination 2015
Investment [Line Items]
Total commercial mortgage loans	586	589
Year of Origination 2014
Investment [Line Items]
Total commercial mortgage loans	479	490
Year of Origination 2013 and prior
Investment [Line Items]
Total commercial mortgage loans	$ 1,358	$ 1,451