Accounting Policies - Inventories (Details) - USD ($) $ in Billions	Mar. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Inventory valuation allowance	$ 1.6	$ 1.6

Amount of valuation reserve for inventory.

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Name:	us-gaap_InventoryValuationReserves
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant