Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenue	$ 3,968	$ 3,504	$ 12,388	$ 11,238
Expense:
Compensation and benefits	2,437	2,083	7,256	6,442
Other operating expenses	1,064	880	3,047	2,656
Operating expenses	3,501	2,963	10,303	9,098
Operating income	467	541	2,085	2,140
Other net benefit credits	69	63	203	194
Interest income	4	2	34	8
Interest expense	(133)	(69)	(394)	(198)
Cost of extinguishment of debt	0	0	(32)	0
Investment income (loss)	7	(52)	20	(24)
Acquisition related derivative contracts	0	(100)	(8)	(100)
Income before income taxes	414	385	1,908	2,020
Income tax expense	108	106	531	509
Net income before non-controlling interests	306	279	1,377	1,511
Less: Net income attributable to non-controlling interests	3	3	26	14
Net income attributable to the Company	$ 303	$ 276	$ 1,351	$ 1,497
Net income per share attributable to the Company:
Basic net income per share attributable to the Company (usd per share)	$ 0.60	$ 0.55	$ 2.67	$ 2.96
Diluted net income per share attributable to the Company (usd per share)	$ 0.59	$ 0.54	$ 2.64	$ 2.93
Average number of shares outstanding:
Average number of shares outstanding - Basic (in shares)	506	504	506	506
Average number of shares outstanding - Diluted (in shares)	511	510	511	512
Shares outstanding (in shares)	505	504	505	504