Investments - Mortgage Loans, Net Past Due (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Financing Receivable, 90 Days or More Past Due, Still Accruing	$ 25	$ 0
Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	591	1,041
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	162	8
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	541	164
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	1,701	563
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	938	1,802
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,034	991
Mortgage loan valuation allowance	78	79
Mortgage loans, before allowance for credit losses	4,967	4,569
Commercial mortgage loans
Financing Receivable, Past Due [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	1,043	1,913
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,529	1,478
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	1,010	130
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	2,675	1,012
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	4,429	2,662
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,982	4,420
Mortgage loan valuation allowance	172	167
Mortgage loans, before allowance for credit losses	12,668	11,615
Commercial mortgage loans, excluding loans under development | Commercial mortgage loans
Financing Receivable, Past Due [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	1,027	1,807
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,529	1,478
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	1,010	130
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	2,572	1,012
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	4,398	2,563
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,849	4,393
Mortgage loans, before allowance for credit losses	12,385	11,383
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	542	955
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	121	6
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	458	141
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	1,594	485
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	789	1,730
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	911	942
Mortgage loans, before allowance for credit losses	4,415	4,259
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	1,043	1,913
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,529	1,452
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	985	130
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	2,653	987
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	4,424	2,617
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,982	4,400
Mortgage loans, before allowance for credit losses	12,616	11,499
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	49	68
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	10	1
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	24	8
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	31	26
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	38	34
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	90	16
Mortgage loans, before allowance for credit losses	242	153
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	0	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	0	5
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	22	25
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	5	45
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0	20
Mortgage loans, before allowance for credit losses	27	95
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	0	15
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	3	0
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	8	3
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	15	9
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	66	16
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	16	7
Mortgage loans, before allowance for credit losses	108	50
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	0	3
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	28	1
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	51	12
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	61	43
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	45	22
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	17	26
Mortgage loans, before allowance for credit losses	202	107
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial mortgage loans
Financing Receivable, Past Due [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	0	21
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	25	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	0	0
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	0	0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0	0
Mortgage loans, before allowance for credit losses	$ 25	$ 21