Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Revenue	$ 3,364	$ 3,338	$ 13,211	$ 12,893	$ 12,951
Expense:
Compensation and benefits			7,461	7,334	7,515
Other operating expenses			3,086	3,140	3,135
Operating expenses			10,547	10,474	10,650
Operating income	633	594	2,664	2,419	2,301
Interest income			5	13	21
Interest expense			(189)	(163)	(165)
Cost of extinguishment of debt			0	0	(137)
Investment income			1	38	37
Income before income taxes			2,480	2,307	2,057
Income tax expense			685	671	586
Income from continuing operations	441	380	1,795	1,636	1,471
Discontinued operations, net of tax	0	1	0	0	26
Net income before non-controlling interests			1,795	1,636	1,497
Less: Net income attributable to non-controlling interests			27	37	32
Net income attributable to the Company	$ 436	$ 375	$ 1,768	$ 1,599	$ 1,465
Basic Per Share Data:
Basic net income per share – Continuing operations (in dollars per share)	$ 0.85	$ 0.72	$ 3.41	$ 3.01	$ 2.64
Net income attributable to the Company (in dollars per share)	0.85	0.72	3.41	3.01	2.69
Diluted Per Share Data:
Continuing operations (in dollars per share)	0.84	0.71	3.38	2.98	2.61
Net income attributable to the Company (in dollars per share)	$ 0.84	$ 0.71	$ 3.38	$ 2.98	$ 2.65
Average number of shares outstanding
Basic (in shares)			519	531	545
Diluted (in shares)			524	536	553
Shares outstanding at December 31 (in shares)	514	522	514	522	540