Revenue Recognition - Schedule of Contract Balances (Details) $ in Millions	3 Months Ended
	Dec. 31, 2019 USD ($)
Contract With Customer, Balance [Roll Forward]
Opening balance, September 30, 2019	$ 157
Closing balance, December 31, 2019	183
Increase (decrease)	26
Receivable From Clients [Member]
Contract With Customer, Balance [Roll Forward]
Opening balance, September 30, 2019	25
Closing balance, December 31, 2019	54
Increase (decrease)	29
Receivable From Affiliates [Member]
Contract With Customer, Balance [Roll Forward]
Opening balance, September 30, 2019	7
Closing balance, December 31, 2019	8
Increase (decrease)	1
Other Receivables [Member]
Contract With Customer, Balance [Roll Forward]
Opening balance, September 30, 2019	125
Closing balance, December 31, 2019	121
Increase (decrease)	$ (4)