Goodwill and Other Intangible Assets - Components of Goodwill (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($)
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	$ 10,957
Accumulated impairment losses, beginning balance	(492)
Goodwill, net, beginning balance	10,465
Foreign exchange	(9)
Goodwill, gross, ending balance	10,946
Accumulated impairment losses, ending balance	(492)
Goodwill, net, ending balance	10,454
Goodwill disposed of during the period	(4)
Acquisition accounting adjustment	2
HCB [Member]
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	4,300
Accumulated impairment losses, beginning balance	(130)
Goodwill, net, beginning balance	4,170
Foreign exchange	(5)
Goodwill, gross, ending balance	4,295
Accumulated impairment losses, ending balance	(130)
Goodwill, net, ending balance	4,165
Goodwill disposed of during the period	0
Acquisition accounting adjustment	0
CRB [Member]
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	2,308
Accumulated impairment losses, beginning balance	(362)
Goodwill, net, beginning balance	1,946
Foreign exchange	(4)
Goodwill, gross, ending balance	2,300
Accumulated impairment losses, ending balance	(362)
Goodwill, net, ending balance	1,938
Goodwill disposed of during the period	(4)
Acquisition accounting adjustment	0
IRR [Member]
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	1,792
Accumulated impairment losses, beginning balance	0
Goodwill, net, beginning balance	1,792
Foreign exchange	0
Goodwill, gross, ending balance	1,794
Accumulated impairment losses, ending balance	0
Goodwill, net, ending balance	1,794
Goodwill disposed of during the period	0
Acquisition accounting adjustment	2
BDA [Member]
Goodwill [Roll Forward]
Goodwill, gross, beginning balance	2,557
Accumulated impairment losses, beginning balance	0
Goodwill, net, beginning balance	2,557
Foreign exchange	0
Goodwill, gross, ending balance	2,557
Accumulated impairment losses, ending balance	0
Goodwill, net, ending balance	2,557
Goodwill disposed of during the period	0
Acquisition accounting adjustment	$ 0