Annual and transition report of foreign private issuers pursuant to Section 13 or 15(d)

Equity (Narrative) (Details)

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Equity (Narrative) (Details) - USD ($)
1 Months Ended 2 Months Ended 12 Months Ended
Mar. 09, 2018
Jan. 31, 2018
Mar. 02, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Feb. 28, 2018
Oct. 31, 2017
Jul. 31, 2017
May 31, 2017
Feb. 28, 2017
Nov. 30, 2016
Aug. 31, 2016
May 31, 2016
Feb. 28, 2016
Equity, Class of Treasury Stock [Line Items]                              
Treasury stock acquired (in shares)       23,732,835                      
Treasury stock acquired, average price per share (in USD per share)       $ 47.39                      
Shares cancelled (in shares)       20,000,000                      
Subsequent Event [Member]                              
Equity, Class of Treasury Stock [Line Items]                              
Share repurchase, remaining amount under the program     $ 145,700,000                        
Treasury stock acquired (in shares)     4,076,603                        
Treasury stock acquired, average price per share (in USD per share)     $ 52.40                        
Shares cancelled (in shares) 6,000,000 5,000,000                          
Ordinary share capital                              
Equity, Class of Treasury Stock [Line Items]                              
Share repurchase program, authorized amount               $ 200,000,000 $ 250,000,000 $ 300,000,000 $ 350,000,000 $ 250,000,000 $ 250,000,000 $ 250,000,000 $ 400,000,000
Shares cancelled (in shares)       20,000,000 15,563,862 9,698,588                  
Ordinary share capital | Subsequent Event [Member]                              
Equity, Class of Treasury Stock [Line Items]                              
Share repurchase program, authorized amount             $ 200,000,000