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		145	145			145
Net earnings (losses) including portion attributable to nonredeemable noncontrolling interest		144						(1)
Other comprehensive income (loss)		(287)	(287)				(287)
Dividends		(31)	(31)			(31)
Shares issued:
Exercise of stock options, shares				374,314
Exercise of stock options		14	14		14
Restricted stock awards, shares				200,625
Other benefit plans, shares				52,583
Other benefit plans		6	6		6
Dividend reinvestment plan, shares				2,779
Stock-based compensation expense		5	5		5
Shares exchanged — benefit plans, shares				(23,882)
Shares exchanged — benefit plans		(3)	(3)			(3)
Forfeitures of restricted stock, shares				(666)
Other		0						0
Ending Balance, shares at Mar. 31, 2018				88,881,213
Ending Balance at Mar. 31, 2018		5,183	5,183		1,294	3,584	305	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		(3)
Ending Balance, Redeemable Noncontrolling Interests at Mar. 31, 2018		$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change	[1]						(221)
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		329	329			329
Net earnings (losses) including portion attributable to nonredeemable noncontrolling interest		329						0
Other comprehensive income (loss)		396	396				396
Dividends		(36)	(36)			(36)
Shares issued:
Exercise of stock options, shares				152,253
Exercise of stock options		6	6		6
Restricted stock awards, shares				232,565
Other benefit plans, shares				11,062
Other benefit plans		1	1		1
Dividend reinvestment plan, shares				1,893
Dividend reinvestment plan		0	0		0
Stock-based compensation expense		6	6		6
Shares exchanged — benefit plans, shares				(43,470)
Shares exchanged — benefit plans		(4)	(4)		(1)	(3)
Forfeitures of restricted stock, shares				(8,314)
Other		$ (5)	(3)			(3)		(2)
Ending Balance, shares at Mar. 31, 2019		89,637,713		89,637,713
Ending Balance at Mar. 31, 2019		$ 5,665	$ 5,665		$ 1,346	$ 3,875	$ 444	$ 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		(3)
Other		3
Ending Balance, Redeemable Noncontrolling Interests at Mar. 31, 2019		$ 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.