Insurance - Narrative (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Insurance [Line Items]
Carrying value of cash and securities owned by U.S.-based insurance subsidiaries on deposit	$ 1,000				$ 1,000
Carrying value of cash and securities owned by insurance subsidiaries on deposit in support of underwriting activities at Lloyd's	215				215
Undrawn letters of credit	332				332
Undrawn letters of credit, collateralized	0				$ 0
Workers' compensation insurance discount rate					4.50%	4.50%
Workers' compensation insurance discount, which has reduced the liability for unpaid losses and loss adjustment expenses	16				$ 16	$ 18
Long-term care insurance reserves, net of reinsurance recoverables	37				37	34
Investment in Federal Home Loan Bank capital stock	44				44
Proceeds received under funding agreements with the Federal Home Loan Bank	200				150
Advances from Federal Home Loan Bank	935				$ 935
Description of variable rate basis					LIBOR
Repayments of advances from Federal Home Loan Bank due in year two	285				$ 285
Repayments of advances from Federal Home Loan Bank due in year four	500				500
Repayments of advances from Federal Home Loan Bank due in year five	150				150
Fair value of mortgage-backed securities held as collateral by the Federal Home Loan Bank	1,080				1,080
Interest on advances from Federal Home Loan Bank					8	3	$ 1
Maximum amount of dividends available to be paid by insurance subsidiaries to AFG without prior approval of regulatory authorities	693				693
Dividends on Common Stock					(187)	(178)	(169)
Aggregate guaranteed minimum death benefit value on variable annuity polices in force	20				20	27
Minimum
Insurance [Line Items]
Dividends payments without violating the most restrictive debt covenants, minimum	1,000				$ 1,000
Minimum | LIBOR
Insurance [Line Items]
FHLB advances, basis spread on variable rate					0.03%
Maximum | LIBOR
Insurance [Line Items]
FHLB advances, basis spread on variable rate					0.53%
Average | LIBOR
Insurance [Line Items]
FHLB advances, basis spread on variable rate					1.18%
Catastrophe Bonds
Insurance [Line Items]
Catastrophe reinsurance coverage, annual cost					$ 5
Life insurance
Insurance [Line Items]
Life insurance in force, ceded premiums	10,220				10,220	11,190
Life insurance in force, direct premiums	$ 13,490				13,490	14,670
Life written premiums ceded					31	40	41
Reinsurance recoveries					41	50	59
Variable annuities | Maximum
Insurance [Line Items]
Death benefits paid in excess of the variable annuity account balances (are less than in 2014, 2015 and 2016)					1	1	1
Property and casualty insurance | Other lines
Insurance [Line Items]
Special charges related to the exit of certain lines of business within subsidiaries			$ 65
Special charges to increase asbestos and environmental reserves		$ 36		$ 67	$ 36	$ 67	$ 24
Property and casualty insurance | Other lines | Increased insurance loss reserves related to medical malpractice and general liability lines
Insurance [Line Items]
Special charges related to the exit of certain lines of business within subsidiaries			$ 57