Investments - Mortgage Loans, Debt Service Coverage Ratio (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 18,209	$ 15,938
Commercial mortgage loans
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	2,155	1,913
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,384	1,478
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	1,047	130
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	2,721	1,012
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	4,284	2,662
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,961	4,420
Mortgage loans, net of allowances	13,387	11,448
Mortgage loans, before allowance for credit losses	13,552	11,615
Commercial mortgage loans | Commercial mortgage loans, excluding loans under development
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	2,077	1,807
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,384	1,478
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	1,047	130
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	2,618	1,012
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	4,255	2,563
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,863	4,393
Mortgage loans, before allowance for credit losses	13,244	11,383
Commercial mortgage loans | Commercial mortgage loans, excluding loans under development | Greater than 1.20x
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	1,523	1,274
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,259	1,369
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	797	129
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	2,126	846
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	2,546	2,440
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,147	2,964
Mortgage loans, before allowance for credit losses	9,398	9,022
Commercial mortgage loans | Commercial mortgage loans, excluding loans under development | 1.00x – 1.20x
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	554	533
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	105	101
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	30	1
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	135	70
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	954	36
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	546	1,122
Mortgage loans, before allowance for credit losses	2,324	1,863
Commercial mortgage loans | Commercial mortgage loans, excluding loans under development | Less than 1.00x
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	20	8
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	220	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	357	96
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	755	87
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	170	307
Mortgage loans, before allowance for credit losses	$ 1,522	$ 498