Financing Receivables - Credit Quality Information - Financial Advisor Loans (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	[1]
Financing receivables - credit quality information
Allowance for credit losses	$ 51	$ 68	$ 71	$ 51
Commercial Loans
Financing receivables - credit quality information
Allowance for credit losses	48	66	$ 67	$ 51
Commercial Loans | Loans to financial advisors
Amortized cost basis by year of origination and loan-to-value ratio
Originated in Current Fiscal Year	106	171
Originated in Fiscal Year before Latest Fiscal Year	155	137
Originated Two Years before Latest Fiscal Year	124	101
Originated Three Years before Latest Fiscal Year	91	128
Originated Four Years before Latest Fiscal Year	120	84
Originated Five or More Years before Latest Fiscal Year	135	94
Total amortized cost basis	731	715
Commercial Loans | Loans to financial advisors | Active
Amortized cost basis by year of origination and loan-to-value ratio
Originated in Current Fiscal Year	104	171
Originated in Fiscal Year before Latest Fiscal Year	155	137
Originated Two Years before Latest Fiscal Year	124	101
Originated Three Years before Latest Fiscal Year	91	127
Originated Four Years before Latest Fiscal Year	119	83
Originated Five or More Years before Latest Fiscal Year	128	86
Total amortized cost basis	721	705
Commercial Loans | Loans to financial advisors | Terminated
Financing receivables - credit quality information
Allowance for credit losses	6	7
Amortized cost basis by year of origination and loan-to-value ratio
Originated in Current Fiscal Year	2
Originated Three Years before Latest Fiscal Year		1
Originated Four Years before Latest Fiscal Year	1	1
Originated Five or More Years before Latest Fiscal Year	7	8
Total amortized cost basis	$ 10	$ 10

[1] Prior to January 1, 2020, the allowance for credit losses was based on an incurred loss model that did not require estimating expected credit losses over the expected life of the asset.