Investments - Mortgage Loans, Loan to Value Ratio (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net of allowances	$ 14,591	$ 14,306
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	1,496
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,567
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	131
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	1,047
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	2,750
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	4,399
Mortgage loans, net of allowances	11,158	10,505
Mortgage loans, before allowance for credit losses	11,390	10,515
Commercial mortgage loans \| Commercial mortgage loans, excluding loans under development
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	1,414
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,567
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	131
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	1,047
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	2,657
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	4,378
Mortgage loans, net of allowances		10,412
Mortgage loans, before allowance for credit losses	11,194	10,422
Commercial mortgage loans \| Commercial mortgage loans, excluding loans under development \| Less than 50%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	282
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,250
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	45
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	200
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	207
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	611
Mortgage loans, net of allowances		2,640
Mortgage loans, before allowance for credit losses	2,595
Commercial mortgage loans \| Commercial mortgage loans, excluding loans under development \| 50% to 60%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	249
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	162
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	40
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	277
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	733
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,215
Mortgage loans, net of allowances		2,486
Mortgage loans, before allowance for credit losses	2,676
Commercial mortgage loans \| Commercial mortgage loans, excluding loans under development \| 61% to 70%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	539
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	71
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	46
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	475
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	1,430
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,978
Mortgage loans, net of allowances		4,093
Mortgage loans, before allowance for credit losses	4,539
Commercial mortgage loans \| Commercial mortgage loans, excluding loans under development \| 71% to 80%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	331
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	45
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	95
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	287
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	574
Mortgage loans, net of allowances		1,162
Mortgage loans, before allowance for credit losses	1,332
Commercial mortgage loans \| Commercial mortgage loans, excluding loans under development \| 81% to 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	13
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	0
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	0
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		$ 31
Mortgage loans, before allowance for credit losses	13
Commercial mortgage loans \| Commercial mortgage loans, excluding loans under development \| Greater than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	39
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	0
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, before allowance for credit losses	$ 39

Amount of financing receivable originated more than five years prior to current fiscal year.

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Amount of financing receivable originated in current fiscal year.

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Amount of financing receivable originated in fiscal year prior to current fiscal year.

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Amount of financing receivable originated three years prior to current fiscal year.

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Amount of financing receivable originated two years prior to current fiscal year.

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The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

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Amount, before allowance for credit loss, of financing receivable.

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