Schedule II - Condensed Financial Information, Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Cash and cash equivalents	$ 2,972	$ 3,185	$ 1,968	$ 1,420
Short-term investments	199	691
Other assets	2,316	2,227
Total assets	61,753	59,360
Liabilities:
Short-term debt	240	276
Long-term debt	5,199	4,756
Total liabilities	47,969	45,575
Shareholders Equity:
Common stock (shares issued, 296; authorized, 600)	74	74
Additional paid-in capital	2,940	2,892
Accumulated other comprehensive loss	(1,082)	(1,382)
Retained earnings	15,824	13,855
Less: treasury stock, at cost	(4,021)	(1,716)
Total shareholders' equity	13,735	13,723
Total liabilities and equity	61,753	59,360
Parent Company [Member]
Assets
Cash and cash equivalents	9	18	$ 16	$ 51
Short-term investments	63	57
Investments in subsidiaries	22,655	20,315
Intercompany receivable	200	173
Other assets	252	415
Total assets	23,179	20,978
Liabilities:
Intercompany payable	2,980	998
Short-term debt	231	257
Long-term debt	5,112	4,658
Other liabilities	1,121	1,342
Total liabilities	9,444	7,255
Shareholders Equity:
Common stock (shares issued, 296; authorized, 600)	74	74
Additional paid-in capital	2,940	2,892
Accumulated other comprehensive loss	(1,082)	(1,382)
Retained earnings	15,824	13,855
Less: treasury stock, at cost	(4,021)	(1,716)
Total shareholders' equity	13,735	13,723
Total liabilities and equity	$ 23,179	$ 20,978