Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenue	$ 4,189	$ 4,349	$ 8,840	$ 8,420
Expense:
Compensation and benefits	2,429	2,537	4,984	4,819
Other operating expenses	875	1,132	1,901	1,983
Operating expenses	3,304	3,669	6,885	6,802
Operating income	885	680	1,955	1,618
Other net benefit credits	63	70	127	134
Interest income	2	2	4	30
Interest expense	(132)	(141)	(259)	(261)
Cost of extinguishment of debt	0	(32)	0	(32)
Investment (loss) income	(31)	8	(33)	13
Acquisition related derivative contracts	0	(37)	0	(8)
Income before income taxes	787	550	1,794	1,494
Income tax expense	207	206	447	423
Net income before non-controlling interests	580	344	1,347	1,071
Less: Net income attributable to non-controlling interests	8	12	21	23
Net income attributable to the Company	$ 572	$ 332	$ 1,326	$ 1,048
Net income per share attributable to the Company:
Basic net income per share attributable to the Company (usd per share)	$ 1.13	$ 0.66	$ 2.62	$ 2.07
Diluted net income per share attributable to the Company (usd per share)	$ 1.12	$ 0.65	$ 2.60	$ 2.05
Average number of shares outstanding:
Average number of shares outstanding - Basic (in shares)	506	507	505	506
Average number of shares outstanding - Diluted (in shares)	511	512	510	511
Shares outstanding (in shares)	506	507	506	507