Investments - Mortgage Loans (Details) - Commercial Real Estate - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Mortgage Loans on Real Estate [Line Items]
New mortgage loans	$ 8	$ 41
Mortgage loans fully repaid	44	52
Mortgage loans foreclosed	$ 0	$ 0

Amount of decrease in investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate, from foreclosure.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Footnote 6))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

Name:	us-gaap_MortgageLoansOnRealEstateForeclosures
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration