Insurance - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other lines | Property and Casualty Insurance
Insurance [Line Items]
Special charges to increase asbestos and environmental reserves	$ 18	$ 89	$ 18	$ 89