Goodwill and Other Intangible Assets - Components of Goodwill (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($)
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	$ 11,686
Accumulated impairment losses, beginning balance	(492)
Goodwill, net, beginning balance	11,194
Goodwill acquired	43
Goodwill disposals	(1)
Acquisition accounting adjustment	(5)
Foreign exchange	(35)
Goodwill, gross, ending balance	11,688
Accumulated impairment losses, ending balance	(492)
Goodwill, net, ending balance	11,196
HCB [Member]
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	4,298
Accumulated impairment losses, beginning balance	(130)
Goodwill, net, beginning balance	4,168
Goodwill acquired	15
Goodwill disposals	0
Acquisition accounting adjustment	0
Foreign exchange	(13)
Goodwill, gross, ending balance	4,300
Accumulated impairment losses, ending balance	(130)
Goodwill, net, ending balance	4,170
CRB [Member]
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	2,309
Accumulated impairment losses, beginning balance	(362)
Goodwill, net, beginning balance	1,947
Goodwill acquired	28
Goodwill disposals	(1)
Acquisition accounting adjustment	0
Foreign exchange	(9)
Goodwill, gross, ending balance	2,327
Accumulated impairment losses, ending balance	(362)
Goodwill, net, ending balance	1,965
IRR [Member]
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	1,795
Accumulated impairment losses, beginning balance	0
Goodwill, net, beginning balance	1,795
Goodwill acquired	0
Goodwill disposals	0
Acquisition accounting adjustment	0
Foreign exchange	(13)
Goodwill, gross, ending balance	1,782
Accumulated impairment losses, ending balance	0
Goodwill, net, ending balance	1,782
BDA [Member]
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	3,284
Accumulated impairment losses, beginning balance	0
Goodwill, net, beginning balance	3,284
Goodwill acquired	0
Goodwill disposals	0
Acquisition accounting adjustment	(5)
Foreign exchange	0
Goodwill, gross, ending balance	3,279
Accumulated impairment losses, ending balance	0
Goodwill, net, ending balance	$ 3,279