Employee Benefits - Components of Net Periodic (Benefit) Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	27	24	81	74
Expected return on plan assets, net of administration expenses	(34)	(36)	(102)	(108)
Amortization of prior-service cost	1	0	2	1
Amortization of net actuarial loss	13	15	40	45
Net periodic (benefit) cost	7	3	21	12
Loss on pension settlement	0	0	0	0
Total net periodic (benefit) cost	7	3	21	12
U.K.
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	26	26	81	84
Expected return on plan assets, net of administration expenses	(46)	(46)	(143)	(147)
Amortization of prior-service cost	0	1	1	1
Amortization of net actuarial loss	7	6	22	21
Net periodic (benefit) cost	(13)	(13)	(39)	(41)
Loss on pension settlement	0	9	0	32
Total net periodic (benefit) cost	(13)	(4)	(39)	(9)
Other
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	6	6	20	20
Expected return on plan assets, net of administration expenses	(9)	(11)	(29)	(34)
Amortization of prior-service cost	0	0	0	0
Amortization of net actuarial loss	3	3	9	9
Net periodic (benefit) cost	0	(2)	0	(5)
Loss on pension settlement	0	0	0	0
Total net periodic (benefit) cost	$ 0	$ (2)	$ 0	$ (5)