Business Dispositions - Carrying Value of Assets and Liabilities to be Transferred in Sale (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Assets	$ 167	$ 0
Disposal Group, Including Discontinued Operation, Liabilities, Total	153	$ 0
Continental Europe Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents	138
Disposal Group, Including Discontinued Operation, Other Assets	29
Disposal Group, Including Discontinued Operation, Assets	167
Disposal Group, Including Discontinued Operation, Unpaid losses and loss adjustment expenses	74
Disposal Group, Including Discontinued Operation, Deferred Revenue	35
Disposal Group, Including Discontinued Operation, Other Liabilities	44
Disposal Group, Including Discontinued Operation, Liabilities, Total	153
Disposal Group, Including Discontinued Operation, Consideration	14
Continental Europe Operations [Member] | Fair Value, Recurring [Member] | Fixed Maturities and Short-Term Investments [Member] | Available-for-sale Securities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets Held-for-sale, Long Lived, Fair Value Disclosure	80
Continental Europe Operations [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Recurring [Member] | Fixed Maturities and Short-Term Investments [Member] | Available-for-sale Securities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets Held-for-sale, Long Lived, Fair Value Disclosure	2
Continental Europe Operations [Member] | Significant Observable Inputs (Level 2) | Fair Value, Recurring [Member] | Fixed Maturities and Short-Term Investments [Member] | Available-for-sale Securities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets Held-for-sale, Long Lived, Fair Value Disclosure	78
Continental Europe Operations [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Nonrecurring [Member] | Fixed Maturities and Short-Term Investments [Member] | Available-for-sale Securities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets Held-for-sale, Long Lived, Fair Value Disclosure	$ 66