Consolidated Statement of Changes in Equity (Unaudited) - USD ($) $ in Millions		Total	Total	Common Shares	Common Stock and Capital Surplus	Retained Earnings	Accumulated Other Comp. Income (Loss)	Noncontrolling interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change		$ 4	$ 4			$ 225	$ (221)
Beginning Balance, shares at Dec. 31, 2017				88,275,460
Beginning Balance at Dec. 31, 2017		5,331	5,330		$ 1,269	3,248	813	$ 1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (losses) attributable to parent		559	559			559
Net earnings (losses) including portion attributable to nonredeemable noncontrolling interest		558						(1)
Other comprehensive income (loss), attributable to parent			(548)				(548)
Other comprehensive income (loss) including portion attributable to nonredeemable noncontrolling interest		(548)
Dividends		(227)	(227)			(227)
Shares issued:
Exercise of stock options, shares				635,364
Exercise of stock options		23	23		23
Restricted stock awards, shares				200,625
Other benefit plans, shares				86,229
Other benefit plans		10	10		10
Dividend reinvestment plan, shares				21,072
Dividend reinvestment plan		2	2		2
Stock-based compensation expense		17	17		17
Shares exchanged — benefit plans, shares				(26,520)
Shares exchanged — benefit plans		(3)	(3)		(1)	(2)
Forfeitures of restricted stock, shares				(3,522)
Other		(3)	(3)			(3)		0
Ending Balance, shares at Sep. 30, 2018				89,188,708
Ending Balance at Sep. 30, 2018		5,164	5,164		1,320	3,800	44	0
Beginning Balance, Redeemable Noncontrolling Interests at Dec. 31, 2017		3
Redeemable Noncontrolling Interest, Equity, Carrying Amount [Abstract]
Net earnings attributable to redeemable noncontrolling interests		(6)
Other		3
Ending Balance, Redeemable Noncontrolling Interests at Sep. 30, 2018		0
Beginning Balance, shares at Jun. 30, 2018				89,072,114
Beginning Balance at Jun. 30, 2018		5,084	5,084		1,309	3,628	147	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (losses) attributable to parent		204	204			204
Net earnings (losses) including portion attributable to nonredeemable noncontrolling interest		204						0
Other comprehensive income (loss), attributable to parent			(103)				(103)
Other comprehensive income (loss) including portion attributable to nonredeemable noncontrolling interest		(103)
Dividends		(31)	(31)			(31)
Shares issued:
Exercise of stock options, shares				103,638
Exercise of stock options		4	4		4
Restricted stock awards, shares				0
Other benefit plans, shares				12,553
Other benefit plans		2	2		2
Dividend reinvestment plan, shares				3,066
Dividend reinvestment plan		0	0		0
Stock-based compensation expense		6	6		6
Shares exchanged — benefit plans, shares				(2,210)
Shares exchanged — benefit plans		(1)	(1)		(1)	0
Forfeitures of restricted stock, shares				(453)
Other		(1)	(1)			(1)		0
Ending Balance, shares at Sep. 30, 2018				89,188,708
Ending Balance at Sep. 30, 2018		5,164	5,164		1,320	3,800	44	0
Beginning Balance, Redeemable Noncontrolling Interests at Jun. 30, 2018		0
Redeemable Noncontrolling Interest, Equity, Carrying Amount [Abstract]
Net earnings attributable to redeemable noncontrolling interests		(1)
Other		1
Ending Balance, Redeemable Noncontrolling Interests at Sep. 30, 2018		$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change	[1]						0
Beginning Balance, shares at Dec. 31, 2018		89,291,724		89,291,724
Beginning Balance at Dec. 31, 2018		$ 4,972	4,970		1,334	3,588	48	2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (losses) attributable to parent		686	686			686
Net earnings (losses) including portion attributable to nonredeemable noncontrolling interest		686						0
Other comprehensive income (loss), attributable to parent			869				869
Other comprehensive income (loss) including portion attributable to nonredeemable noncontrolling interest		869
Dividends		(242)	(242)			(242)
Shares issued:
Exercise of stock options, shares				591,233
Exercise of stock options		25	25		25
Restricted stock awards, shares				232,635
Other benefit plans, shares				58,488
Other benefit plans		6	6		6
Dividend reinvestment plan, shares				11,059
Dividend reinvestment plan		1	1		1
Stock-based compensation expense		17	17		17
Shares exchanged — benefit plans, shares				(47,069)
Shares exchanged — benefit plans		(5)	(5)		(1)	(4)
Forfeitures of restricted stock, shares				(10,647)
Other		$ (8)	(6)			(6)		(2)
Ending Balance, shares at Sep. 30, 2019		90,127,423		90,127,423
Ending Balance at Sep. 30, 2019		$ 6,321	6,321		1,382	4,022	917	0
Beginning Balance, Redeemable Noncontrolling Interests at Dec. 31, 2018		0
Redeemable Noncontrolling Interest, Equity, Carrying Amount [Abstract]
Net earnings attributable to redeemable noncontrolling interests		(8)
Other comprehensive income (loss) attributable to redeemable noncontrolling interests		2
Other		6
Ending Balance, Redeemable Noncontrolling Interests at Sep. 30, 2019		0
Beginning Balance, shares at Jun. 30, 2019				89,917,601
Beginning Balance at Jun. 30, 2019		6,090	6,090		1,367	3,914	809	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (losses) attributable to parent		147	147			147
Net earnings (losses) including portion attributable to nonredeemable noncontrolling interest		147						0
Other comprehensive income (loss), attributable to parent			108				108
Other comprehensive income (loss) including portion attributable to nonredeemable noncontrolling interest		108
Dividends		(36)	(36)			(36)
Shares issued:
Exercise of stock options, shares				191,227
Exercise of stock options		8	8		8
Restricted stock awards, shares				70
Other benefit plans, shares				17,345
Other benefit plans		2	2		2
Dividend reinvestment plan, shares				1,570
Dividend reinvestment plan		0	0		0
Stock-based compensation expense		5	5		5
Shares exchanged — benefit plans, shares				(80)
Shares exchanged — benefit plans		0	0		0	0
Forfeitures of restricted stock, shares				(310)
Other		$ (3)	(3)			(3)		0
Ending Balance, shares at Sep. 30, 2019		90,127,423		90,127,423
Ending Balance at Sep. 30, 2019		$ 6,321	$ 6,321		$ 1,382	$ 4,022	917	$ 0
Beginning Balance, Redeemable Noncontrolling Interests at Jun. 30, 2019		0
Redeemable Noncontrolling Interest, Equity, Carrying Amount [Abstract]
Net earnings attributable to redeemable noncontrolling interests		(4)
Other comprehensive income (loss) attributable to redeemable noncontrolling interests		1
Other		3
Ending Balance, Redeemable Noncontrolling Interests at Sep. 30, 2019		$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change	[1]						$ 0

[1] On January 1, 2018, AFG adopted new guidance that requires all equity securities other than those accounted for under the equity method to be reported at fair value with holding gains and losses recognized in net earnings. At the date of adoption, the $221 million net unrealized gain on equity securities classified as available for sale (with unrealized holding gains and losses reported in AOCI) under the prior guidance was reclassified from AOCI to retained earnings as the cumulative effect of an accounting change.