Insurance - Narrative (Details) - USD ($) $ in Millions	3 Months Ended								6 Months Ended	12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Insurance [Line Items]
Carrying value of cash and securities owned by U.S.-based insurance subsidiaries on deposit	$ 1,120									$ 1,120
Undrawn letters of credit	308									308
Undrawn letters of credit, collateralized	0									$ 0
Workers' compensation insurance discount rate										3.50%	4.50%
Workers' compensation insurance discount, which has reduced the liability for unpaid losses and loss adjustment expenses	9				$ 12					$ 9	$ 12
Pretax COVID-19 related losses			$ 105	$ 10						115
Prior year claims and claims adjustment expense	8	$ 0	$ 77	$ 42	45	$ 12	$ 41	$ 45		127	143
Long-term care insurance reserves, net of reinsurance recoverables	52				46					52	46
Dividends on common stock										(336)	(446)	$ (397)
Dividends payments without violating the most restrictive debt covenants, minimum	2,000									2,000
Catastrophe reinsurance coverage, excess retention amount										50
Catastrophe reinsurance coverage, retention amount										100
Ceded annuity receipts										492	0	0
Ceded annuity surrenders, benefits and withdrawals										206	0	0
Aggregate guaranteed minimum death benefit value on variable annuity polices in force	11				13					11	13
Retained Earnings
Insurance [Line Items]
Dividends on common stock										(336)	(446)	(397)
Allowance for reinsurance recoverables
Insurance [Line Items]
Net expense reduction against the allowance for losses on reinsurance recoverables												2
Maximum
Insurance [Line Items]
Maximum amount of dividends available to be paid by insurance subsidiaries to AFG without prior approval of regulatory authorities	705									$ 705
Maximum | Allowance for reinsurance recoverables
Insurance [Line Items]
Net expense reduction against the allowance for losses on reinsurance recoverables											1
Catastrophe Bonds
Insurance [Line Items]
Catastrophe reinsurance coverage, excess retention percentage										95.00%
Catastrophe reinsurance coverage, excess retention amount										$ 200
Catastrophe reinsurance coverage, retention amount										109
Catastrophe reinsurance coverage, annual cost										11
Life insurance
Insurance [Line Items]
Life insurance in force, ceded premiums	5,420				6,230					5,420	6,230
Life insurance in force, direct premiums	8,330				9,530					8,330	9,530
Reinsurance ceded										19	20	22
Reinsurance recoveries										28	32	38
Variable annuities | Maximum
Insurance [Line Items]
Death benefits paid in excess of the variable annuity account balances										1	1	1
Neon exited lines charge
Insurance [Line Items]
Prior year claims and claims adjustment expense										19	7	0
Property and casualty insurance | Other lines
Insurance [Line Items]
Special A&E charges		$ 47				$ 18				47	18	18
Neon Capital Limited | Property and casualty insurance | Other lines
Insurance [Line Items]
Pretax COVID-19 related losses									$ 20	20
Great American Life Insurance Company
Insurance [Line Items]
Investment in Federal Home Loan Bank capital stock	56									56
Proceeds advanced from Federal Home Loan										200
Repayments of advances from Federal Home Loan Bank										165
Advances from Federal Home Loan Bank	1,130				1,100					1,130	1,100
Repayments of advances from Federal Home Loan Bank due in next twelve months	931									931
Repayments of advances from Federal Home Loan Bank due in year five	200									200
Fair value of fixed maturity investments held as collateral by the Federal Home Loan Bank	$ 1,370									1,370
Interest on advances from Federal Home Loan Bank										$ 11	27	$ 20
Quota share coinsurance percentage										0.50
Inforce Annuity Business, Ceded, Percent of Total Inforce	15.00%
Deferred Loss on Ceded Reserves	$ 180
Amortization of deferred loss on reinsurance	11
Ceded annuity receipts										$ 492
Ceded annuity surrenders, benefits and withdrawals										206
Commission and expense allowances received from reinsurance contracts										39
Amount of annuity benefits expense reduction from reinsurance contracts										$ 46
Great American Life Insurance Company | Block Reinsurance
Insurance [Line Items]
Ceded Inforce Annuity Business	$ 5,960
Great American Life Insurance Company | Minimum
Insurance [Line Items]
Interest rates on Federal Home Loan Bank advances	0.31%									0.31%
Expected Life of Ceded Reserves	7 years
Great American Life Insurance Company | Maximum
Insurance [Line Items]
Interest rates on Federal Home Loan Bank advances	1.35%									1.35%
Expected Life of Ceded Reserves	10 years
Great American Life Insurance Company | Average
Insurance [Line Items]
Interest rates on Federal Home Loan Bank advances	0.53%									0.53%
Great American Life Insurance Company | FHLB, advances, refinanced terms
Insurance [Line Items]
Advances from Federal Home Loan Bank					$ 610						610
Great American Life Insurance Company | Life insurance
Insurance [Line Items]
Increases in statutory surplus from reinsurance treaty										$ 139	$ 124