Business Combination (Narrative) (Details) - USD ($)			12 Months Ended
	Jul. 09, 2020	Jul. 31, 2018	Dec. 31, 2020	Oct. 31, 2020	Dec. 31, 2019	Apr. 30, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Interest acquired	33.30%
Common stock, shares issued (in shares)	5,200,000		265,198,371		236,547,842
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01	$ 0.01	$ 0.01
Silversea Cruises
Business Acquisition [Line Items]
Interest acquired	33.30%		33.30%
Common stock, shares issued (in shares)	5,200,000
Silversea Cruises
Business Acquisition [Line Items]
Percentage of business acquired		66.70%					66.70%
Payments to acquire business		$ 1,020,000,000.00
Contingent consideration		44,000,000.0
Silversea Cruises
Business Acquisition [Line Items]
Long-term debt		$ 700,000,000				$ 700,000,000