Schedule I - Parent Company Financial Information (Condensed Balance Sheets) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 1,935	$ 1,138	$ 1,306	$ 1,377
Investment securities	7,598	8,090
Other current assets	4,011	2,122
Total current assets	14,712	12,300
Property and equipment, net	1,419	1,218
Other long-term assets	1,675	1,774
Total assets	23,466	20,735
Current liabilities:
Book overdraft	334	403
Total current liabilities	7,355	6,323
Long-term debt	3,825	2,600
Other long-term liabilities	291	289
Total liabilities	13,820	11,419
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; 197,951,551 shares issued at December 31, 2014 and 196,275,506 shares issued at December 31, 2013	33	33
Capital in excess of par value	2,330	2,267
Retained earnings	9,916	8,942
Accumulated other comprehensive income	223	158
Treasury stock, at cost, 48,347,541 shares at December 31, 2014 and 42,245,097 shares at December 31, 2013	(2,856)	(2,084)
Total stockholders' equity	9,646	9,316	8,847	8,063
Total liabilities and stockholders' equity	23,466	20,735
Parent Company
Current assets:
Cash and cash equivalents	1,211	161	151	187
Investment securities	201	347
Receivable from operating subsidiaries	873	777
Other current assets	180	186
Total current assets	2,465	1,471
Property and equipment, net	885	709
Investments in subsidiaries	13,983	12,959
Other long-term assets	114	82
Total assets	17,447	15,221
Current liabilities:
Payable to operating subsidiaries	3,130	2,570
Current portion of notes payable to operating subsidiaries	28	28
Book overdraft	54	59
Other current liabilities	562	452
Total current liabilities	3,774	3,109
Long-term debt	3,825	2,600
Notes payable to operating subsidiaries	9	9
Other long-term liabilities	193	187
Total liabilities	7,801	5,905
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; 197,951,551 shares issued at December 31, 2014 and 196,275,506 shares issued at December 31, 2013	33	33
Capital in excess of par value		2,267
Retained earnings		8,942
Accumulated other comprehensive income		158
Treasury stock, at cost, 48,347,541 shares at December 31, 2014 and 42,245,097 shares at December 31, 2013	(2,856)	(2,084)
Total stockholders' equity	9,646	9,316
Total liabilities and stockholders' equity	$ 17,447	$ 15,221