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		355	355			355
Net earnings (losses) including portion attributable to nonredeemable noncontrolling interest		354						(1)
Other comprehensive income (loss), attributable to parent			(445)				(445)
Other comprehensive income (loss) including portion attributable to nonredeemable noncontrolling interest		(445)
Dividends		(196)	(196)			(196)
Shares issued:
Exercise of stock options, shares				531,726
Exercise of stock options		19	19		19
Restricted stock awards, shares				200,625
Other benefit plans, shares				73,676
Other benefit plans		8	8		8
Dividend reinvestment plan, shares				18,006
Dividend reinvestment plan		2	2		2
Stock-based compensation expense		11	11		11
Shares exchanged — benefit plans, shares				(24,310)
Shares exchanged — benefit plans		2	2			2
Forfeitures of restricted stock, shares				(3,069)
Other		(2)	(2)			(2)		0
Ending Balance, shares at Jun. 30, 2018				89,072,114
Ending Balance at Jun. 30, 2018		5,084	5,084		1,309	3,628	147	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		(5)
Other		2
Ending Balance, Redeemable Noncontrolling Interests at Jun. 30, 2018		0
Beginning Balance, shares at Mar. 31, 2018				88,881,213
Beginning Balance at Mar. 31, 2018		5,183	5,183		1,294	3,584	305	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (losses) attributable to parent		210	210			210
Net earnings (losses) including portion attributable to nonredeemable noncontrolling interest		210						0
Other comprehensive income (loss), attributable to parent			(158)				(158)
Other comprehensive income (loss) including portion attributable to nonredeemable noncontrolling interest		(158)
Dividends		(165)	(165)			(165)
Shares issued:
Exercise of stock options, shares				157,412
Exercise of stock options		5	5		5
Restricted stock awards, shares				0
Other benefit plans, shares				21,093
Other benefit plans		2	2		2
Dividend reinvestment plan, shares				15,227
Dividend reinvestment plan		2	2		2
Stock-based compensation expense		6	6		6
Shares exchanged — benefit plans, shares				(428)
Shares exchanged — benefit plans		1	1		0	1
Forfeitures of restricted stock, shares				(2,403)
Other		(2)	(2)			(2)		0
Ending Balance, shares at Jun. 30, 2018				89,072,114
Ending Balance at Jun. 30, 2018		5,084	5,084		1,309	3,628	147	0
Beginning Balance, Redeemable Noncontrolling Interests at Mar. 31, 2018		0
Redeemable Noncontrolling Interest, Equity, Carrying Amount [Abstract]
Net earnings attributable to redeemable noncontrolling interests		2
Other		2
Ending Balance, Redeemable Noncontrolling Interests at Jun. 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		539	539			539
Net earnings (losses) including portion attributable to nonredeemable noncontrolling interest		539						0
Other comprehensive income (loss), attributable to parent			761				761
Other comprehensive income (loss) including portion attributable to nonredeemable noncontrolling interest		761
Dividends		(206)	(206)			(206)
Shares issued:
Exercise of stock options, shares				400,006
Exercise of stock options		17	17		17
Restricted stock awards, shares				232,565
Other benefit plans, shares				41,143
Other benefit plans		4	4		4
Dividend reinvestment plan, shares				9,489
Dividend reinvestment plan		1	1		1
Stock-based compensation expense		12	12		12
Shares exchanged — benefit plans, shares				(46,989)
Shares exchanged — benefit plans		5	5		1	4
Forfeitures of restricted stock, shares				(10,337)
Other		$ (5)	(3)			(3)		(2)
Ending Balance, shares at Jun. 30, 2019		89,917,601		89,917,601
Ending Balance at Jun. 30, 2019		$ 6,090	6,090		1,367	3,914	809	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		(4)
Other comprehensive income (loss) attributable to redeemable noncontrolling interests		1
Other		3
Ending Balance, Redeemable Noncontrolling Interests at Jun. 30, 2019		0
Beginning Balance, shares at Mar. 31, 2019				89,637,713
Beginning Balance at Mar. 31, 2019		5,665	5,665		1,346	3,875	444	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (losses) attributable to parent		210	210			210
Net earnings (losses) including portion attributable to nonredeemable noncontrolling interest		210						0
Other comprehensive income (loss), attributable to parent			365				365
Other comprehensive income (loss) including portion attributable to nonredeemable noncontrolling interest		365
Dividends		(170)	(170)			(170)
Shares issued:
Exercise of stock options, shares				247,753
Exercise of stock options		11	11		11
Restricted stock awards, shares				0
Other benefit plans, shares				30,081
Other benefit plans		3	3		3
Dividend reinvestment plan, shares				7,596
Dividend reinvestment plan		1	1		1
Stock-based compensation expense		6	6		6
Shares exchanged — benefit plans, shares				(3,519)
Shares exchanged — benefit plans		1	1		0	1
Forfeitures of restricted stock, shares				(2,023)
Other		$ 0				0		0
Ending Balance, shares at Jun. 30, 2019		89,917,601		89,917,601
Ending Balance at Jun. 30, 2019		$ 6,090	$ 6,090		$ 1,367	$ 3,914	809	$ 0
Beginning Balance, Redeemable Noncontrolling Interests at Mar. 31, 2019		0
Redeemable Noncontrolling Interest, Equity, Carrying Amount [Abstract]
Net earnings attributable to redeemable noncontrolling interests		(1)
Other comprehensive income (loss) attributable to redeemable noncontrolling interests		1
Other		0
Ending Balance, Redeemable Noncontrolling Interests at Jun. 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.