SCHEDULE I - PARENT COMPANY FINANCIAL INFORMATION (Condensed Statements of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	$ 2,262	$ 5,639	$ 5,284
Cash flows from investing activities:
Acquisitions, net of cash and cash equivalents acquired	(4,187)	(709)	0
Purchases of investment securities	(7,197)	(9,125)	(6,361)
Proceeds from sale of investment securities	3,547	2,747	4,086
Proceeds from maturities of investment securities	2,597	4,986	1,733
Purchases of property and equipment, net	(1,316)	(964)	(736)
Net cash used in investing activities	(6,556)	(3,065)	(1,278)
Cash flows from financing activities:
Proceeds from issuance of senior notes, net	2,984	1,088	987
Repayment of senior notes	0	(400)	(400)
Proceeds (repayments) from issuance of commercial paper, net	352	295	(360)
Proceeds from term loan	2,500	1,000	0
Repayment of term loan	(2,078)	(1,000)	(650)
Change in book overdraft	6	95	54
Common stock repurchases	(79)	(1,820)	(1,070)
Dividends paid	(354)	(323)	(291)
Proceeds from stock option exercises & other	21	49	58
Net cash provided by (used in) financing activities	3,015	(1,955)	(2,295)
(Decrease) increase in cash and cash equivalents	(1,279)	619	1,711
Cash and cash equivalents at beginning of period	4,673	4,054	2,343
Cash and cash equivalents at end of period	3,394	4,673	4,054
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	2,853	2,531	3,529
Cash flows from investing activities:
Acquisitions, net of cash and cash equivalents acquired	(4,187)	(709)	0
Capital contributions to operating subsidiaries	(2,580)	(538)	(423)
Purchases of investment securities	(200)	(460)	(204)
Proceeds from sale of investment securities	71	13	15
Proceeds from maturities of investment securities	122	411	134
Purchases of property and equipment, net	(958)	(785)	(585)
Net cash used in investing activities	(7,732)	(2,068)	(1,063)
Cash flows from financing activities:
Proceeds from issuance of senior notes, net	2,953	1,088	987
Repayment of senior notes	0	(400)	(400)
Proceeds (repayments) from issuance of commercial paper, net	352	295	(360)
Proceeds from term loan	2,500	1,000	0
Repayment of term loan	0	(1,000)	(650)
Change in book overdraft	(52)	80	2
Common stock repurchases	(79)	(1,820)	(1,070)
Dividends paid	(354)	(323)	(291)
Proceeds from stock option exercises & other	29	47	57
Net cash provided by (used in) financing activities	5,349	(1,033)	(1,725)
(Decrease) increase in cash and cash equivalents	470	(570)	741
Cash and cash equivalents at beginning of period	436	1,006	265
Cash and cash equivalents at end of period	$ 906	$ 436	$ 1,006