Income Taxes - Narrative (Details) £ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 GBP (£)
Income Tax Reconciliation [Line Items]
Statutory rate of income taxes	21.00%	21.00%	21.00%
Income tax expense (benefit)	$ 127	$ 239	$ 122
Effective income tax rate reconciliation, percent, excluding the Impact of the sale of subsidiaries	21.00%
Income (losses) subject to tax in foreign jurisdictions	$ (131)	(109)	(69)
Operating loss carryforwards, valuation allowance	15
Interest on income taxes accrued	0	0
Amount of expense for penalties related to a tax position	0
Cash payments for income taxes	$ 179	278	156
Limitation on the use of tax credit carryforwards	A SRLY NOL can be used only by the entity that created it and only in years that both it and the consolidated group have taxable income. Approximately $23 million of AFG’s SRLY NOLs expired unutilized at December 31, 2020.
Neon Capital Limited
Income Tax Reconciliation [Line Items]
Income tax expense (benefit)	$ (72)
Income tax benefit, portion attributable to current taxes payable	(65)
AFG
Income Tax Reconciliation [Line Items]
Income tax expense (benefit)	127	239	122
Unrecognized tax benefits that would impact the effective tax rate	0	0
Interest included in tax provision	0	0
Income tax penalties accrued	0	0
Charge for valuation allowance
Income Tax Reconciliation [Line Items]
Charge for valuation allowance against deferred tax assets		118
Maximum | AFG
Income Tax Reconciliation [Line Items]
Interest included in tax provision			1
Amount of expense for penalties related to a tax position		$ 1	$ 1
Amount unutilized
Income Tax Reconciliation [Line Items]
Operating loss carryforwards	23
United Kingdom
Income Tax Reconciliation [Line Items]
Operating loss carryforwards	$ 34			£ 25