Investments - Mortgage Loans, Net Past Due (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest		$ 67,000,000
Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	$ 414,000,000
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	9,000,000
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	171,000,000
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	587,000,000
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	1,929,000,000
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,059,000,000
Mortgage loan valuation allowance	96,000,000	1,000,000
Mortgage loans, before allowance for credit losses	4,169,000,000	4,455,000,000
Commercial mortgage loans
Financing Receivable, Past Due [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	1,496,000,000
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,567,000,000
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	131,000,000
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	1,047,000,000
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	2,750,000,000
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	4,399,000,000
Mortgage loan valuation allowance	232,000,000	10,000,000
Financing Receivable, Past Due		0
Mortgage loans, before allowance for credit losses	11,390,000,000	10,515,000,000
Commercial mortgage loans, excluding loans under development | Commercial mortgage loans
Financing Receivable, Past Due [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	1,414,000,000
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,567,000,000
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	131,000,000
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	1,047,000,000
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	2,657,000,000
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	4,378,000,000
Mortgage loans, before allowance for credit losses	11,194,000,000	$ 10,422,000,000
Financial Asset, 1 to 29 Days Past Due [Member] | Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	384,000,000
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	7,000,000
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	144,000,000
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	507,000,000
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	1,852,000,000
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,016,000,000
Financing Receivable, Not Past Due	3,910,000,000
Financial Asset, 1 to 29 Days Past Due [Member] | Commercial mortgage loans
Financing Receivable, Past Due [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	1,398,000,000
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,546,000,000
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	131,000,000
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	1,047,000,000
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	2,750,000,000
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	4,399,000,000
Financing Receivable, Not Past Due	11,271,000,000
Financial Asset, 30 to 59 Days Past Due [Member] | Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	23,000,000
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	0
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	8,000,000
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	39,000,000
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	35,000,000
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	20,000,000
Financing Receivable, Past Due	125,000,000
Financial Asset, 30 to 59 Days Past Due [Member] | Commercial mortgage loans
Financing Receivable, Past Due [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	98,000,000
Mortgage loans, before allowance for credit losses	98,000,000
Financial Asset, 60 to 89 Days Past Due [Member] | Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	6,000,000
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	0
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	6,000,000
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	9,000,000
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	21,000,000
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	11,000,000
Financing Receivable, Past Due	53,000,000
Financial Asset, 60 to 89 Days Past Due [Member] | Commercial mortgage loans
Financing Receivable, Past Due [Line Items]
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	21,000,000
Mortgage loans, before allowance for credit losses	21,000,000
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	1,000,000
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	2,000,000
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	13,000,000
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	32,000,000
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	21,000,000
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	12,000,000
Financing Receivable, Past Due	$ 81,000,000