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Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2018
Accounting Policies [Abstract] |
Schedule Of Property Software And Equipment Depreciation Periods | Property, software and equipment are depreciated over the following periods:
Fixed Asset |  | Depreciation Period
Buildings and land improvements |  | 5 - 40 years
Computer hardware and software |  | 2 - 7 years
Furniture and equipment |  | 3 - 10 years
Land improvements |  | 3 - 20 years
Leasehold improvements |  | 1 - 20 years
Schedule Of Amortization Period For Intangible Assets | Intangible assets are amortized using the straight-line method over the following periods:
Intangible Asset |  | Amortization Period
Purchased contract rights |  | 5 - 15 years
Provider contracts |  | 4 - 15 years
Customer relationships |  | 3 - 15 years
Trade names |  | 7 - 20 years
Developed technologies |  | 2 - 7 years
Schedule Of Allowance For Uncollectible Accounts | Activity in the allowance for uncollectible accounts for the years ended December 31, is summarized below ($ in millions):
| 2018 |  | 2017 |  | 2016
Allowances, beginning of year | $ | 24 |  |  | $ | 29 |  |  | $ | 10 |
Amounts charged to expense | 134 |  |  | 35 |  |  | 33 |
Write-offs of uncollectible receivables | (35 | ) |  | (40 | ) |  | (14 | )
Allowances, end of year | $ | 123 |  |  | $ | 24 |  |  | $ | 29 |

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