Acquisitions and Sale of Businesses - Allocation of the purchase price of subsidiary (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Nov. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisitions [Line Items]
Total purchase price		$ 3	$ 0	$ 36
Goodwill		$ 207	$ 207	$ 207	$ 199
ABA Insurance Services
Business Acquisitions [Line Items]
Total purchase price	$ 30
Tangible assets acquired	28
Liabilities acquired	26
Net tangible assets acquire, at fair value	2
Excess purchase price over net tangible assets acquired	28
Intangible assets acquired	25
Deferred tax on intangible assets acquired	(5)
Goodwill	$ 8