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Significant Accounting Policies (Details) - USD ($) | 9 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2018 | May 03, 2007
SIP expense - Year of grant |  |  |  | 50.00%
SIP expense - Remaining vesting period |  |  |  | 50.00%
SIP expense - Employees over 59 in year of grant |  |  |  | 100.00%
Percent of shares cancelled post employment |  |  |  | 50.00%
Over 59 percent of shares eligible |  |  |  | 100.00%
U.S. Treasury Securities | $ 3,800,000,000 |  | $ 4,200,000,000 |
Securities Purchased Under Agreement to Resell Segregated for Regulatory Purposes | 17,500,000,000 |  | 11,400,000,000 |
Equity method investments | 22,000,000 |  | 23,000,000 |
Equity Securities without Readily Determinable Fair Value, Amount | 5,000,000 |  | 25,000,000 |
Equity Securities, FV-NI | $ 43,000,000 |  | 0 |
Property and equipment useful lives, description | Computer equipment is depreciated over three to five years and office furniture and equipment are depreciated over five to seven years. Intangible assets with a finite life are amortized on a straight-line basis over their estimated useful lives of three years, and tested for recoverability whenever events indicate that the carrying amounts may not be recoverable. Qualifying costs for internally developed software are capitalized and amortized over the expected useful life of the developed software, not to exceed three years. |  |  |
Restructuring and Related Cost, Incurred Cost | $ 0 | $ 0 |  |
Exchange Cleared [Member] | Equity Securities [Member] |  |  |  |
Investments at cost | $ 3,000,000 |  | $ 5,000,000 |
Maximum [Member] | Computer Equipment [Member] |  |  |  |
Property and equipment useful lives | 5 years |  |  |
Maximum [Member] | Office Furniture And Equipment [Member] |  |  |  |
Property and equipment useful lives | 7 years |  |  |
Maximum [Member] | Internally Developed Software [Member] |  |  |  |
Intangible assets useful lives | 3 years |  |  |
Maximum [Member] | Finite-Lived Intangible Assets [Member] |  |  |  |
Intangible assets useful lives | 3 years |  |  |
Minimum [Member] | Computer Equipment [Member] |  |  |  |
Property and equipment useful lives | 3 years |  |  |
Minimum [Member] | Office Furniture And Equipment [Member] |  |  |  |
Property and equipment useful lives | 5 years |  |  |

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