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Fair Value Measurements (Narrative) (Details) (USD $)
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3 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
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Mar. 31, 2012
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Mar. 31, 2011
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Mar. 31, 2012
April 2021 Senior Unsecured Notes [Member]
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Dec. 31, 2011
April 2021 Senior Unsecured Notes [Member]
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Mar. 31, 2011
April 2021 Senior Unsecured Notes [Member]
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Mar. 31, 2012
Senior Unsecured Notes Due In December Two Thousand Fourteen December Two Thousand Sixteen December Two Thousand Twenty One December Two Thousand Forty One [Member]
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Jan. 17, 2012
Senior Unsecured Notes Due In December Two Thousand Fourteen December Two Thousand Sixteen December Two Thousand Twenty One December Two Thousand Forty One [Member]
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Dec. 31, 2011
Senior Unsecured Notes Due In December Two Thousand Fourteen December Two Thousand Sixteen December Two Thousand Twenty One December Two Thousand Forty One [Member]
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Mar. 31, 2012
Convertible Notes Payable [Member]
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Dec. 31, 2011
Convertible Notes Payable [Member]
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| Debt Instrument [Line Items] | ||||||||||
| Carrying value, convertible notes | $ 2,940,000,000 | $ 2,920,000,000 | ||||||||
| Carrying value, senior unsecured notes | 992,300,000 | 992,100,000 | 3,690,000,000 | 3,690,000,000 | ||||||
| Fair value, convertible notes | 3,990,000,000 | 3,530,000,000 | ||||||||
| Fair Value, senior unsecures notes | 1,060,000,000 | 1,060,000,000 | 3,890,000,000 | 3,930,000,000 | ||||||
| Principal amount, senior unsecured notes | 1,000,000,000 | 3,700,000,000 | 3,700,000,000 | |||||||
| Weighted-average expected life of underlying student loans minimum, years | 2 | |||||||||
| Weighted-average expected life of underlying student loans maximum, years | 7 | |||||||||
| Annual discount rate used in discounted cash flow model | 2.18% | |||||||||
| Auction rate reset, lower range, in days | 7 | |||||||||
| Auction rate reset, upper range, in days | 14 | |||||||||
| Auction rate securities year of maturity, lower range | 2025 | |||||||||
| Auction rate securities year of maturity, higher range | 2040 | |||||||||
| Auction rate securities annual interest rate, lower range | 0.12% | |||||||||
| Auction rate securities annual interest rate, higher range | 0.77% | |||||||||
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings | $ (40,096,000) | $ 1,246,000 | ||||||||