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Dividends (Details) - USD ($)
$ / shares in Units, $ in Millions
Feb. 21, 2018
Nov. 14, 2017
Aug. 22, 2017
May 24, 2017
Feb. 21, 2017
Nov. 15, 2016
Aug. 23, 2016
May 18, 2016
Feb. 23, 2016
Subsequent Event [Line Items]                  
Dividend per share (usd per share)   $ 0.540 $ 0.540 $ 0.540 $ 0.540 $ 0.540 $ 0.540 $ 0.540 $ 0.540
Total amount declared   $ 577 $ 296 $ 297 $ 295 $ 294 $ 295 $ 294 $ 295
Subsequent event                  
Subsequent Event [Line Items]                  
Dividend per share (usd per share) $ 0.54