Consolidated Statements of Changes in Shareholders' Equity - USD ($) shares in Thousands, $ in Millions	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Retained Earnings	AOCI	Noncontrolling Interests
Beginning balance, Shares at Dec. 31, 2014			720,698
Beginning balance at Dec. 31, 2014	$ 24,377	$ 2,603	$ 3,603	$ 6,517	$ 12,317	$ (751)	$ 88
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	2,123				2,084		39
OCI	(277)					(277)
Stock transactions:
Issued in business combinations, Shares			54,000
Issued in business combinations	2,188		$ 270	1,918
Issued in connection with equity awards, net, Shares			5,639
Issued in connection with equity awards, net	62		$ 29	33
Excess tax benefits in connection with equity awards	11			11
Purchase of additional ownership interest in AmRisc, LP	(222)			(219)			(3)
Cash dividends declared on common stock	(789)				(789)
Cash dividends declared on preferred stock	(148)				(148)
Equity-based compensation expense	106			106
Other, net	(91)			(1)			(90)
Ending balance, Shares at Dec. 31, 2015			780,337
Ending balance at Dec. 31, 2015	27,340	2,603	$ 3,902	8,365	13,464	(1,028)	34
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	2,442				2,426		16
OCI	(104)					(104)
Stock transactions:
Issued in business combinations, Shares			31,665
Issued in business combinations	1,063		$ 158	905
Issued in connection with equity awards, net, Shares			9,241
Issued in connection with equity awards, net	220		$ 46	174
Excess tax benefits in connection with equity awards	7			7
Issued in connection with preferred stock offerings	450	450
Repurchase of common stock, Shares			(11,768)
Repurchase of common stock	(520)		$ (59)	(461)
Cash dividends declared on common stock	(925)				(925)
Cash dividends declared on preferred stock	(167)				(167)
Equity-based compensation expense	115			115
Other, net	$ 5			(1)	11		(5)
Ending balance, Shares at Dec. 31, 2016	809,475		809,475
Ending balance at Dec. 31, 2016	$ 29,926	3,053	$ 4,047	9,104	14,809	(1,132)	45
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	2,415				2,394		21
OCI	(88)					(88)
Stock transactions:
Issued in business combinations	0
Issued in connection with equity awards, net, Shares			8,059
Issued in connection with equity awards, net	120		$ 41	79
Repurchase of common stock, Shares			(35,528)
Repurchase of common stock	(1,613)		$ (178)	(1,435)
Cash dividends declared on common stock	(1,005)				(1,005)
Cash dividends declared on preferred stock	(174)				(174)
Equity-based compensation expense	132			132
Reclassification of certain tax effects	0				247	(247)
Other, net	$ (18)			13	(12)		(19)
Ending balance, Shares at Dec. 31, 2017	782,006		782,006
Ending balance at Dec. 31, 2017	$ 29,695	$ 3,053	$ 3,910	$ 7,893	$ 16,259	$ (1,467)	$ 47