Employee Benefit Plans - Level 3 Rollforward (Details) - UNITED KINGDOM - Pension Plan [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		$ 1,989		$ 2,368
Foreign Currency Exchange Rate Changes		81		120
Ending balance		2,151		1,989		$ 2,368
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	[1]	239
Ending balance	[1]	243		239
Real Estate Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		239
Ending balance		243		239
Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance		239	[1]	230		105
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held		(5)		23		6
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Purchase, Sale, and Settlement		0		0		104
Foreign Currency Exchange Rate Changes		9		(14)		15
Ending balance		$ 243	[1]	$ 239	[1]	$ 230

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