Consolidated Statement of Changes in Equity - USD ($) $ in Millions	Total	Total	Common Shares	Common Stock and Capital Surplus	Retained Earnings	Accumulated Other Comprehensive Inc. (Loss)		Noncontrolling Interests
Beginning Balance, shares at Dec. 31, 2015			87,474,452
Beginning Balance at Dec. 31, 2015	$ 4,770	$ 4,592		$ 1,301	$ 2,987	$ 304		$ 178
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to parent	649	649			649
Net income (loss), including portion attributable to nonredeemable noncontrolling interest	668							19
Other comprehensive income (loss)	67	62				62		5
Dividends	(187)	(187)			(187)
Shares issued:
Exercise of stock options, shares			958,344
Exercise of stock options	32	32		32
Restricted stock awards, shares			318,940
Restricted stock awards	0	0		0
Other benefit plans, shares			95,875
Other benefit plans	7	7		7
Dividend reinvestment plan, shares			25,516
Dividend reinvestment plan	2	2		2
Stock-based compensation: Expense	22	22		22
Shares acquired and retired, shares			(1,911,976)
Shares acquired and retired	(133)	(133)		(29)	(104)
Shares exchanged — benefit plans, shares			(32,707)
Shares exchanged — benefit plans	(2)	(2)		0	(2)
Forfeitures of restricted stock, shares			(4,045)
Forfeitures of restricted stock	0	0		0
Acquisition of noncontrolling interests	(315)	(128)		(137)		9	[1]	(187)
Other	(12)				0			(12)
Ending Balance, shares at Dec. 31, 2016			86,924,399
Ending Balance at Dec. 31, 2016	4,919	4,916		1,198	3,343	375		3
Beginning Balance, Redeemable Noncontrolling Interests at Dec. 31, 2015	0
Ending Balance, Redeemable Noncontrolling Interests at Dec. 31, 2016	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to parent	475	475			475
Net income (loss), including portion attributable to nonredeemable noncontrolling interest	477							2
Other comprehensive income (loss)	296	296				296		0
Impact of the U.S. corporate tax rate change on AOCI	0	0			(145)	145		0
Dividends	(421)	(421)			(421)
Shares issued:
Exercise of stock options, shares			1,020,986
Exercise of stock options	34	34		34
Restricted stock awards, shares			232,250
Restricted stock awards	0	0		0
Other benefit plans, shares			99,588
Other benefit plans	10	10		10
Dividend reinvestment plan, shares			42,572
Dividend reinvestment plan	4	4		4
Stock-based compensation: Expense	24	24		24
Shares exchanged — benefit plans, shares			(37,718)
Shares exchanged — benefit plans	(5)	(5)		(1)	(4)
Forfeitures of restricted stock, shares			(6,617)
Forfeitures of restricted stock	0	0		0
Sale of redeemable noncontrolling interests	(3)	(3)				(3)		0
Other	$ (4)	0			0	0		(4)
Ending Balance, shares at Dec. 31, 2017	88,275,460		88,275,460
Ending Balance at Dec. 31, 2017	$ 5,331	5,330		1,269	3,248	813		1
Ending Balance, Redeemable Noncontrolling Interests at Dec. 31, 2017	3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change	4	4			225	(221)
Redeemable Noncontrolling Interest, Equity, Carrying Amount [Abstract]
Redeemable noncontrolling interests	3
Net income (loss) attributable to parent	530	530			530
Net income (loss), including portion attributable to nonredeemable noncontrolling interest	531							1
Other comprehensive income (loss)	(544)	(544)				(544)		0
Dividends	$ (397)	(397)			(397)
Exercise of stock options, shares	778,270		778,270
Exercise of stock options	$ 29	29		29
Restricted stock awards, shares			200,625
Restricted stock awards	0	0		0
Other benefit plans, shares			103,797
Other benefit plans	12	12		12
Dividend reinvestment plan, shares			29,998
Dividend reinvestment plan	3	3		3
Stock-based compensation: Expense	23	23		23
Shares acquired and retired, shares			(65,589)
Shares acquired and retired	(6)	(6)		(1)	(5)
Shares exchanged — benefit plans, shares			(26,520)
Shares exchanged — benefit plans	(3)	(3)		(1)	(2)
Forfeitures of restricted stock, shares			(4,317)
Forfeitures of restricted stock	0	0		0
Other	$ (11)	(11)			(11)			0
Ending Balance, shares at Dec. 31, 2018	89,291,724		89,291,724
Ending Balance at Dec. 31, 2018	$ 4,972	$ 4,970		$ 1,334	$ 3,588	$ 48		$ 2
Redeemable Noncontrolling Interest, Equity, Carrying Amount [Abstract]
Net income (loss) attributable to redeemable noncontrolling interest	(14)
Shareholders' equity, redeemable noncontrolling interests, other changes	11
Ending Balance, Redeemable Noncontrolling Interests at Dec. 31, 2018	0
Redeemable Noncontrolling Interest, Equity, Carrying Amount [Abstract]
Redeemable noncontrolling interests	$ 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. Other also includes the December 2017 reclassification of $145 million stranded in AOCI from accounting for the Tax Cuts and Jobs Act of 2017 to retained earnings (see Note A — “Accounting Policies — Income Taxes”), the impact on AOCI of the December 2017 sale of redeemable noncontrolling interests in Neon and the November 2016 acquisition of the noncontrolling interest in NATL (see Note B — “Acquisitions and Sale of Businesses”).