Investments - Allowance for Credit Losses (Details) $ in Millions	4 Months Ended	9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2020 USD ($)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provision for loan losses	$ 28
For initial credit losses on purchased loans accounted for as PCD financial assets	7
Ending Balance	35	$ 35
Financing Receivable, Recorded Investment, Aging [Abstract]
Total loans that are 90 days past due and still accruing	0	0
Debt Securities, Available-for-sale, Purchased with Credit Deterioration, Amount at Purchase Price [Abstract]
Purchase price		265
Allowance for credit losses at acquisition		35
Discount (or premiums) attributable to other factors		84
AFS purchased credit-deteriorated par value		384
Residential Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provision for loan losses	26
For initial credit losses on purchased loans accounted for as PCD financial assets	7
Ending Balance	33	33
Financing Receivable, Recorded Investment, Aging [Abstract]
Total loans that are 90 days past due and still accruing	0	0
Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provision for loan losses	2
For initial credit losses on purchased loans accounted for as PCD financial assets	0
Ending Balance	2	2
Financing Receivable, Recorded Investment, Aging [Abstract]
Total loans that are 90 days past due and still accruing	$ 0	$ 0