Financial Instruments - Unobservable Inputs, and Items Measured at Fair Value on a Recurring Basis that Used Significant Unobservable Inputs (Level 3) (Details) - Recurring - Level 3 - Auction rate securities	Jul. 27, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Years to principal recovery	3 years
Illiquidity premium
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Measurement input	0.06
Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Years to principal recovery	2 years
Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Years to principal recovery	12 years