Investments - Components of the net unrealized gain on securities that is included in AOCI in the Balance Sheet (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Unrealized gain on:
Pretax		$ 118	$ 1,063
Deferred Tax		(25)	(223)
Net		93	840
Total investments
Unrealized gain on:
Pretax			1,620
Deferred Tax			(340)
Net			1,280
Total fixed maturities
Unrealized gain on:
Pretax		191	1,341
Deferred Tax		(40)	(282)
Net		151	1,059
Fixed maturities — annuity segment
Unrealized gain on:
Pretax	[1]	143	1,082
Deferred Tax	[1]	(30)	(227)
Net	[1]	113	855
Fixed maturities — all other
Unrealized gain on:
Pretax		48	259
Deferred Tax		(10)	(55)
Net		38	204
Equity securities
Unrealized gain on:
Pretax	[2]		279
Deferred Tax	[2]		(58)
Net	[2]		221
Deferred policy acquisition costs — annuity segment
Unrealized gain on:
Pretax		(56)	(433)
Deferred Tax		12	91
Net		(44)	(342)
Annuity benefits accumulated
Unrealized gain on:
Pretax		(18)	(137)
Deferred Tax		3	29
Net		(15)	(108)
Unearned revenue
Unrealized gain on:
Pretax		1	13
Deferred Tax		0	(3)
Net		$ 1	$ 10

[1] Net unrealized gains on fixed maturity investments supporting AFG’s annuity benefits accumulated.

[2] As discussed in Note A — “Accounting Policies — Investments,” effective January 1, 2018, all equity securities other than those accounted for under the equity method are carried at fair value through net earnings.