Restructuring Costs (Restructuring Activities) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Restructuring Reserve [Roll Forward]
Liability at beginning of period	$ 102	$ 112
Amounts Accrued	20	112
Cash Paid	(64)	(112)
Other	(1)	(10)
Liability at end of period	57	102
Severance
Restructuring Reserve [Roll Forward]
Liability at beginning of period	51	73
Amounts Accrued	6	73
Cash Paid	(45)	(91)
Other	0	(4)
Liability at end of period	12	51
Future rent under non-cancelable leases and other costs
Restructuring Reserve [Roll Forward]
Liability at beginning of period	51	39
Amounts Accrued	14	39
Cash Paid	(19)	(21)
Other	(1)	(6)
Liability at end of period	45	51
Jardine Lloyd Thompson Group plc
Restructuring Reserve [Roll Forward]
Liability at beginning of period	47	0
Amounts Accrued	137	335
Cash Paid	(127)	(265)
Non-cash charges	(24)	(23)
Liability at end of period	33	47
Jardine Lloyd Thompson Group plc | Severance
Restructuring Reserve [Roll Forward]
Liability at beginning of period	42	0
Amounts Accrued	29	154
Cash Paid	(56)	(112)
Non-cash charges	0	0
Liability at end of period	15	42
Jardine Lloyd Thompson Group plc | Real estate related costs
Restructuring Reserve [Roll Forward]
Liability at beginning of period	5	0
Amounts Accrued	31	38
Cash Paid	(4)	(14)
Non-cash charges	(21)	(19)
Liability at end of period	11	5
Jardine Lloyd Thompson Group plc | Information Technology
Restructuring Reserve [Roll Forward]
Liability at beginning of period	0	0
Amounts Accrued	37	45
Cash Paid	(34)	(45)
Non-cash charges	(3)	0
Liability at end of period	0	0
Jardine Lloyd Thompson Group plc | Consulting and other outside services
Restructuring Reserve [Roll Forward]
Liability at beginning of period	0	0
Amounts Accrued	40	98
Cash Paid	(33)	(94)
Non-cash charges	0	(4)
Liability at end of period	$ 7	$ 0