Schedule I - Parent Company Financial Information (Condensed Balance Sheets) (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 4,042	$ 3,877	$ 2,571	$ 1,935
Investment securities	9,557	7,595
Other current assets	2,949	3,438
Total current assets	17,402	16,190
Property and equipment, net	1,584	1,505
Other long-term assets	2,166	2,226
Total assets	27,178	25,396
Current liabilities:
Book overdraft	141	212
Short-term borrowings	150	300
Total current liabilities	9,406	7,822
Long-term debt	4,770	3,792
Other long-term liabilities	237	263
Total liabilities	17,336	14,711
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $1 par; 10,000,000 shares authorized; none issued	0	0
Common stock, $0.16 2/3 par; 300,000,000 shares authorized; 198,572,458 shares issued at December 31, 2017 and 198,495,007 shares issued at December 31, 2016	33	33
Capital in excess of par value	2,445	2,562
Retained earnings	13,670	11,454
Accumulated other comprehensive income (loss)	19	(66)
Treasury stock, at cost, 60,893,762 shares at December 31, 2017 and 49,189,811 shares at December 31, 2016	(6,325)	(3,298)
Total stockholders’ equity	9,842	10,685	10,346	9,646
Total liabilities and stockholders’ equity	27,178	25,396
Parent Company
Current assets:
Cash and cash equivalents	383	1,710	$ 1,389	$ 1,211
Investment securities	305	300
Receivable from operating subsidiaries	1,042	1,136
Other current assets	245	122
Total current assets	1,975	3,268
Property and equipment, net	1,091	1,086
Investments in subsidiaries	16,810	15,276
Other long-term assets	426	374
Total assets	20,302	20,004
Current liabilities:
Payable to operating subsidiaries	4,311	4,107
Current portion of notes payable to operating subsidiaries	28	28
Book overdraft	41	38
Short-term borrowings	150	300
Other current liabilities	896	708
Total current liabilities	5,426	5,181
Long-term debt	4,770	3,792
Notes payable to operating subsidiaries	9	9
Other long-term liabilities	255	337
Total liabilities	10,460	9,319
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $1 par; 10,000,000 shares authorized; none issued	0	0
Common stock, $0.16 2/3 par; 300,000,000 shares authorized; 198,572,458 shares issued at December 31, 2017 and 198,495,007 shares issued at December 31, 2016	33	33
Capital in excess of par value	2,445	2,562
Retained earnings	13,670	11,454
Accumulated other comprehensive income (loss)	19	(66)
Treasury stock, at cost, 60,893,762 shares at December 31, 2017 and 49,189,811 shares at December 31, 2016	(6,325)	(3,298)
Total stockholders’ equity	9,842	10,685
Total liabilities and stockholders’ equity	$ 20,302	$ 20,004