Investments - Allowance for credit losses (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Allowance for Loan and Lease Losses [Roll Forward]
Balance as of January 1	$ 0
Credit losses on securities for which credit losses were not previously recorded	4
Initial allowance for credit losses recognized on financial assets accounted for as PCD	0
Reductions for securities sold during the period	0
Reductions for intent to sell or more likely than not will be required to sell securities prior to recovery of amortized cost	0
Increase (decrease) on securities with allowance recorded in previous period	0
Write-offs	0
Recoveries of amounts previously written off	0
Balance as of March 31	4
Residential mortgage-backed
Allowance for Loan and Lease Losses [Roll Forward]
Balance as of January 1	0
Credit losses on securities for which credit losses were not previously recorded	0
Initial allowance for credit losses recognized on financial assets accounted for as PCD	0
Reductions for securities sold during the period	0
Reductions for intent to sell or more likely than not will be required to sell securities prior to recovery of amortized cost	0
Increase (decrease) on securities with allowance recorded in previous period	0
Write-offs	0
Recoveries of amounts previously written off	0
Balance as of March 31	0
Commercial mortgage-backed
Allowance for Loan and Lease Losses [Roll Forward]
Balance as of January 1	0
Credit losses on securities for which credit losses were not previously recorded	1
Initial allowance for credit losses recognized on financial assets accounted for as PCD	0
Reductions for securities sold during the period	0
Reductions for intent to sell or more likely than not will be required to sell securities prior to recovery of amortized cost	0
Increase (decrease) on securities with allowance recorded in previous period	0
Write-offs	0
Recoveries of amounts previously written off	0
Balance as of March 31	1
Foreign corporate private securities
Allowance for Loan and Lease Losses [Roll Forward]
Balance as of January 1	0
Credit losses on securities for which credit losses were not previously recorded	1
Initial allowance for credit losses recognized on financial assets accounted for as PCD	0
Reductions for securities sold during the period	0
Reductions for intent to sell or more likely than not will be required to sell securities prior to recovery of amortized cost	0
Increase (decrease) on securities with allowance recorded in previous period	0
Write-offs	0
Recoveries of amounts previously written off	0
Balance as of March 31	1
Other Asset-backed Securities [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance as of January 1	0
Credit losses on securities for which credit losses were not previously recorded	2
Initial allowance for credit losses recognized on financial assets accounted for as PCD	0
Reductions for securities sold during the period	0
Reductions for intent to sell or more likely than not will be required to sell securities prior to recovery of amortized cost	0
Increase (decrease) on securities with allowance recorded in previous period	0
Write-offs	0
Recoveries of amounts previously written off	0
Balance as of March 31	$ 2