Employee Benefit Obligations - Fair Value of Assets (Details) - Defined Benefit Pension Plans - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension assets at fair value
Total assets.	$ 5,716.0	$ 5,175.0	$ 6,052.0
US Plan
Pension assets at fair value
Total assets.	2,202.0	1,901.0	2,420.0
US Plan | Fair Value Inputs Level 1 And Level 2
Pension assets at fair value
Total assets.	2,034.0	1,741.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Cash and cash equivalents
Pension assets at fair value
Total assets.	99.0	98.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Consumer discretionary Securities
Pension assets at fair value
Total assets.	83.0	61.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Financials corporate equity securities
Pension assets at fair value
Total assets.	64.0	54.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Healthcare Corporate equity securities
Pension assets at fair value
Total assets.	63.0	49.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Industrials corporate equity securities
Pension assets at fair value
Total assets.	76.0	59.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Information technology corporate equity securities
Pension assets at fair value
Total assets.	111.0	73.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Utilities Equity Securities [Member]
Pension assets at fair value
Total assets.	48.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Other corporate equity securities
Pension assets at fair value
Total assets.	18.0	50.0
US Plan | Fair Value Inputs Level 1 And Level 2 | FHLMC mortgage backed securities
Pension assets at fair value
Total assets.	42.0	40.0
US Plan | Fair Value Inputs Level 1 And Level 2 | FNMA mortgage backed securities
Pension assets at fair value
Total assets.	73.0	65.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Municipal bonds
Pension assets at fair value
Total assets.	27.0	52.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Treasury bonds
Pension assets at fair value
Total assets.	69.0	45.0
US Plan | Fair Value Inputs Level 1 And Level 2 | U.S. government and agency securities-Other
Pension assets at fair value
Total assets.	45.0	10.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Corporate bonds and notes-Communications
Pension assets at fair value
Total assets.	79.0	67.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Corporate bonds and notes-Consumer discretionary
Pension assets at fair value
Total assets.	99.0	80.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Corporate bonds and notes-Consumer staples
Pension assets at fair value
Total assets.	100.0	41.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Corporate bonds and notes-Financials
Pension assets at fair value
Total assets.	261.0	245.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Corporate bonds and notes-Healthcare
Pension assets at fair value
Total assets.	91.0	88.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Corporate bonds and notes-Industrials
Pension assets at fair value
Total assets.	101.0	100.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Corporate bonds and notes-Information technology
Pension assets at fair value
Total assets.	78.0	54.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Corporate bonds and notes-Oil and gas
Pension assets at fair value
Total assets.	91.0	103.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Corporate bonds and notes-Private placement
Pension assets at fair value
Total assets.	62.0	69.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Corporate bonds and notes-Utilities
Pension assets at fair value
Total assets.	101.0	88.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Corporate bonds and notes-Other
Pension assets at fair value
Total assets.	50.0	60.0
US Plan | Fair Value Inputs Level 1 And Level 2 | Commingled funds
Pension assets at fair value
Total assets.	103.0
US Plan | Fair Value Inputs Level 1 And Level 2 | International Commingled Funds
Pension assets at fair value
Total assets.		90.0
US Plan | Level 1
Pension assets at fair value
Total assets.	554.0	410.0
US Plan | Level 1 | Cash and cash equivalents
Pension assets at fair value
Total assets.		1.0
US Plan | Level 1 | Consumer discretionary Securities
Pension assets at fair value
Total assets.	83.0	61.0
US Plan | Level 1 | Financials corporate equity securities
Pension assets at fair value
Total assets.	64.0	54.0
US Plan | Level 1 | Healthcare Corporate equity securities
Pension assets at fair value
Total assets.	63.0	49.0
US Plan | Level 1 | Industrials corporate equity securities
Pension assets at fair value
Total assets.	76.0	59.0
US Plan | Level 1 | Information technology corporate equity securities
Pension assets at fair value
Total assets.	111.0	73.0
US Plan | Level 1 | Utilities Equity Securities [Member]
Pension assets at fair value
Total assets.	48.0
US Plan | Level 1 | Other corporate equity securities
Pension assets at fair value
Total assets.	18.0	50.0
US Plan | Level 1 | Treasury bonds
Pension assets at fair value
Total assets.	69.0	45.0
US Plan | Level 1 | Commingled funds
Pension assets at fair value
Total assets.	22.0
US Plan | Level 1 | International Commingled Funds
Pension assets at fair value
Total assets.		18.0
US Plan | Level 2
Pension assets at fair value
Total assets.	1,480.0	1,331.0
US Plan | Level 2 | Cash and cash equivalents
Pension assets at fair value
Total assets.	99.0	97.0
US Plan | Level 2 | FHLMC mortgage backed securities
Pension assets at fair value
Total assets.	42.0	40.0
US Plan | Level 2 | FNMA mortgage backed securities
Pension assets at fair value
Total assets.	73.0	65.0
US Plan | Level 2 | Municipal bonds
Pension assets at fair value
Total assets.	27.0	52.0
US Plan | Level 2 | U.S. government and agency securities-Other
Pension assets at fair value
Total assets.	45.0	10.0
US Plan | Level 2 | Corporate bonds and notes-Communications
Pension assets at fair value
Total assets.	79.0	67.0
US Plan | Level 2 | Corporate bonds and notes-Consumer discretionary
Pension assets at fair value
Total assets.	99.0	80.0
US Plan | Level 2 | Corporate bonds and notes-Consumer staples
Pension assets at fair value
Total assets.	100.0	41.0
US Plan | Level 2 | Corporate bonds and notes-Financials
Pension assets at fair value
Total assets.	261.0	245.0
US Plan | Level 2 | Corporate bonds and notes-Healthcare
Pension assets at fair value
Total assets.	91.0	88.0
US Plan | Level 2 | Corporate bonds and notes-Industrials
Pension assets at fair value
Total assets.	101.0	100.0
US Plan | Level 2 | Corporate bonds and notes-Information technology
Pension assets at fair value
Total assets.	78.0	54.0
US Plan | Level 2 | Corporate bonds and notes-Oil and gas
Pension assets at fair value
Total assets.	91.0	103.0
US Plan | Level 2 | Corporate bonds and notes-Private placement
Pension assets at fair value
Total assets.	62.0	69.0
US Plan | Level 2 | Corporate bonds and notes-Utilities
Pension assets at fair value
Total assets.	101.0	88.0
US Plan | Level 2 | Corporate bonds and notes-Other
Pension assets at fair value
Total assets.	50.0	60.0
US Plan | Level 2 | Commingled funds
Pension assets at fair value
Total assets.	81.0
US Plan | Level 2 | International Commingled Funds
Pension assets at fair value
Total assets.		72.0
US Plan | NAV
Pension assets at fair value
Total assets.	168.0	160.0
Foreign
Pension assets at fair value
Total assets.	3,514.0	3,274.0	$ 3,632.0
U.K.
Pension assets at fair value
Total assets.	3,457.0	3,195.0
U.K. | Level 1
Pension assets at fair value
Total assets.	2,806.0	2,282.0
U.K. | Level 1 | Cash and cash equivalents
Pension assets at fair value
Total assets.	40.0	20.0
U.K. | Level 1 | Equity commingled funds
Pension assets at fair value
Total assets.	162.0
U.K. | Level 1 | U.K. government bonds
Pension assets at fair value
Total assets.	2,576.0	2,229.0
U.K. | Level 1 | Other.
Pension assets at fair value
Total assets.	28.0	33.0
U.K. | Level 2 | Corporate bonds and notes
Pension assets at fair value
Total assets.	478.0
U.K. | NAV | Investment funds - property
Pension assets at fair value
Total assets.	$ 173.0	$ 913.0