Employee Benefit Plans - Level 3 Rollforward (Details) - UNITED KINGDOM - Pension Plan [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		$ 2,151		$ 1,989
Foreign Currency Exchange Rate Changes		75		81
Ending balance		2,334		2,151		$ 1,989
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	[1]	243
Ending balance	[1]	237		243
Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		243	[1]	239		230
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held		(13)		(5)		23
Foreign Currency Exchange Rate Changes		7		9		(14)
Ending balance		$ 237	[1]	$ 243	[1]	$ 239

[1] Refer to Note 15 for additional discussion regarding the three levels of the fair value hierarchy.