Segments of Operations - Narrative (Details) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2020 USD ($)		Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) segment		Jun. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segment					3
Total premiums earned		$ 1,184		$ 1,200	$ 2,393		$ 2,373
Net investment income		468	[1]	580	1,012	[1]	1,122
Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned		1,184		1,200	2,393		2,373
Net investment income		72	[2]	124	165	[2]	228
Property and casualty insurance underwriting		9		59	96		146
Investment and other income, net		65	[3]	115	149	[3]	210
Other lines | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned	[4]	61		0	132		0
Property and casualty insurance underwriting	[5]	(45)		(1)	(47)		(2)
Neon Capital Limited
Segment Reporting Information [Line Items]
Net investment income					(6)
Neon Capital Limited | Maximum
Segment Reporting Information [Line Items]
Net investment income		1
Neon Capital Limited | Other lines | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned				89			177
Net investment income					(6)
Property and casualty insurance underwriting		(43)		$ (4)	44		$ (14)
Investment and other income, net		(1)			$ (10)
Neon Capital Limited | Other lines | Property and Casualty Insurance | Maximum
Segment Reporting Information [Line Items]
Net investment income		$ 1

[1] Net investment income in the second quarter and first six months of 2020 includes income of less than $1 million and losses of $6 million, respectively, on investments held by the companies that comprise the Neon exited lines due primarily to the $7 million loss in first quarter of 2020 recorded on equity securities that are carried at fair value through net investment income.

[2] Includes income of less than $1 million for the second quarter of 2020 and a loss of $6 million in the Neon exited lines in the first six months of 2020 (primarily from the change in fair value of equity securities).

[3] Includes $1 million and $10 million in the second quarter and first six months of 2020, respectively, in net expenses from the Neon exited lines, before noncontrolling interest.

[4] Represents premiums earned in the Neon exited lines during the second quarter and first six months of 2020. Neon’s $89 million and $177 million in earned premiums during the second quarter and first six months of 2019, respectively, are included in the Specialty casualty sub-segment.

[5] Includes an underwriting loss of $43 million in the second quarter of 2020 and $44 million in the first six months of 2020 in the Neon exited lines. Neon’s $4 million and $14 million underwriting losses in the second quarter and first six months of 2019, respectively, are included in the Specialty casualty sub-segment.