Investments - Mortgage Loans, Debt Service Coverage Ratio (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 15,203	$ 14,306
Commercial mortgage loans
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	11,231	10,505
Mortgage loans, before allowance for credit losses	11,525	10,515
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	1,202
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,651
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	146
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	1,049
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	2,770
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	4,521
Mortgage loans, net of allowances		10,412
Mortgage loans, before allowance for credit losses	11,339	10,422
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	928
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,564
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	146
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	994
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	2,712
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	3,501
Mortgage loans, net of allowances		9,212
Mortgage loans, before allowance for credit losses	9,845
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	274
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	80
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	32
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	58
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,020
Mortgage loans, net of allowances		1,166
Mortgage loans, before allowance for credit losses	1,464
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
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	7
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	23
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0
Mortgage loans, net of allowances		$ 34
Mortgage loans, before allowance for credit losses	$ 30