Allowance for Expected Credit Losses - Activity in the Allowance for Credit Losses for Loans Held for Investment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 74	$ 67
Provision	36	4
Other		(1)
Ending balance	97	$ 70
Senior Secured Bank Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	61
Charge-offs	(5)
Provision	27
Ending balance	83
Other Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	10
Charge-offs	0
Provision	0
Ending balance	10
Commercial Real Estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	2
Charge-offs	0
Provision	2
Ending balance	4
Held-to-Maturity Securities
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	0
Charge-offs	0
Provision	4
Ending balance	4
Off-Balance Sheet Commitments
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	19
Charge-offs	0
Provision	3
Ending balance	22
All Other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1
Charge-offs	0
Provision	0
Ending balance	1
Total Credit Reserve
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	93
Charge-offs	(5)
Provision	36
Ending balance	$ 124