Segments of Operations - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) segment		Mar. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segment	3
Total premiums earned	$ 1,209		$ 1,173
Net investment income	544	[1]	542
Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned	1,209		1,173
Net investment income	93	[2]	104
Property and casualty insurance underwriting	87		87
Investment and other income, net	84	[3]	95
Other lines | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned	71	[4]	0
Property and casualty insurance underwriting	(2)	[5]	(1)
Neon Capital Limited
Segment Reporting Information [Line Items]
Net investment income	(6)
Neon Capital Limited | Other lines | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned			88
Net investment income	(6)
Property and casualty insurance underwriting	(1)		$ 10
Investment and other income, net	$ (9)

[1] Net investment income in the first three months of 2020 includes a loss of $6 million on investments held by the companies that comprise the Neon exited lines due primarily to the $7 million loss recorded on equity securities that are carried at fair value through net investment income.

[2] Includes a net loss of $6 million in the Neon exited lines, primarily from the change in fair value of equity securities.

[3] Includes $9 million in net expenses from the Neon exited lines, before noncontrolling interest.

[4] Represents premiums earned in the Neon exited lines during the first three months of 2020. Neon’s $88 million in earned premiums during the first three months of 2019 are included in the Specialty casualty sub-segment.

[5] Includes a $1 million underwriting loss in the first three months of 2020 in the Neon exited lines. Neon’s $10 million underwriting loss in the first three months of 2019 is included in the Specialty casualty sub-segment.