Employee Incentive Plans (Share Grants And Fair Value) (Details) - USD ($) $ in Millions |
12 Months Ended | 68 Months Ended | 107 Months Ended | |||||
|---|---|---|---|---|---|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
Dec. 31, 2012 |
Mar. 31, 2016 |
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| Employee Incentive Plans [Abstract] | ||||||||
| Shares granted | 1,208,630 | [1] | 1,709,968 | 1,894,046 | 17,284,454 | |||
| Fair Value - Date of Grant | $ 53 | $ 49 | $ 46 | $ 302 | ||||
| Shares Granted IPO to Date | 22,097,098 | |||||||
| Fair Value - Date of Grant IPO to Date | $ 450 | |||||||
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