Investments - Mortgage Loans, Loan to Value Ratio (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net of allowances	$ 14,395	$ 14,306
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Mortgage loans, net of allowances	11,078	10,505
Mortgage loans, before allowance for credit losses	11,421	10,515
Commercial mortgage loans \| Commercial mortgage loans, excluding loans under development
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	1,075
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,725
Financing Receivable, Originated Four Years before Latest Fiscal Year	160
Financing Receivable, Originated Three Years before Latest Fiscal Year	1,050
Financing Receivable, Originated Two Years before Latest Fiscal Year	2,761
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	4,510
Mortgage loans, net of allowances		10,412
Mortgage loans, before allowance for credit losses	11,281	10,422
Commercial mortgage loans \| Commercial mortgage loans, excluding loans under development \| Less than 50%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	149
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1,351
Financing Receivable, Originated Four Years before Latest Fiscal Year	74
Financing Receivable, Originated Three Years before Latest Fiscal Year	147
Financing Receivable, Originated Two Years before Latest Fiscal Year	207
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	760
Mortgage loans, net of allowances		2,640
Mortgage loans, before allowance for credit losses	2,688
Commercial mortgage loans \| Commercial mortgage loans, excluding loans under development \| 50% to 60%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	143
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	172
Financing Receivable, Originated Four Years before Latest Fiscal Year	40
Financing Receivable, Originated Three Years before Latest Fiscal Year	332
Financing Receivable, Originated Two Years before Latest Fiscal Year	786
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,128
Mortgage loans, net of allowances		2,486
Mortgage loans, before allowance for credit losses	2,601
Commercial mortgage loans \| Commercial mortgage loans, excluding loans under development \| 61% to 70%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	441
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	108
Financing Receivable, Originated Four Years before Latest Fiscal Year	46
Financing Receivable, Originated Three Years before Latest Fiscal Year	476
Financing Receivable, Originated Two Years before Latest Fiscal Year	1,481
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	2,023
Mortgage loans, net of allowances		4,093
Mortgage loans, before allowance for credit losses	4,575
Commercial mortgage loans \| Commercial mortgage loans, excluding loans under development \| 71% to 80%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	342
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	54
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	95
Financing Receivable, Originated Two Years before Latest Fiscal Year	287
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	599
Mortgage loans, net of allowances		1,162
Mortgage loans, before allowance for credit losses	1,377
Commercial mortgage loans \| Commercial mortgage loans, excluding loans under development \| 81% to 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	40
Financing Receivable, Originated Four Years before Latest Fiscal Year	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0
Mortgage loans, net of allowances		$ 31
Mortgage loans, before allowance for credit losses	$ 40

Amount of financing receivable originated five or more years prior to latest fiscal year.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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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