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Other Assets (Derivative Instruments Narrative) (Details ) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Mar. 31, 2020
Derivative [Line Items] |  |
Derivative, terminated amount |  | $ 4,100,000,000
Swaps | Hedging |  |
Derivative [Line Items] |  |
Reclassification of hedge loss from AOCI | $ 57,000,000.0 |
Loss on derivative | $ 0 |

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