Business Dispositions - Carrying Value of Assets and Liabilities to be Transferred in Sale (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale	$ 165	$ 177
Disposal Group, Including Discontinued Operation, Liabilities, Total	148	158
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	137	142
Disposal Group, Including Discontinued Operation, Other Assets	28	35
Assets held for sale	165	177
Disposal Group, Including Discontinued Operation, Unpaid losses and loss adjustment expenses	77	84
Disposal Group, Including Discontinued Operation, Deferred Revenue	23	31
Disposal Group, Including Discontinued Operation, Other Liabilities	48	43
Disposal Group, Including Discontinued Operation, Liabilities, Total	148	158
Disposal Group, Including Discontinued Operation, Consideration	14	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	84
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	1	1
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	79	83
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	$ 70