Basis of Presentation (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended
	Dec. 31, 2020	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Goodwill [Line Items]
Expenses incurred by the entity		$ 1,674		$ 1,648	$ 5,025	$ 4,943
CareAR Holdings LLC
Goodwill [Line Items]
Acquisition value	$ 9
Expenses incurred by the entity							$ 1
Minimum
Goodwill [Line Items]
Percentage of fair value over carrying value, goodwill			15.00%
Maximum
Goodwill [Line Items]
Percentage of fair value over carrying value, goodwill			20.00%