Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Effects of Reclassification on Prior Periods) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Consolidated Balance Sheet
Current deferred tax asset		$ 0
Other current assets	$ 199	198
Total current assets	5,044	5,533
Deferred tax assets		1,358
Other assets		1,193
Total assets	18,216	17,793	$ 16,960
Accrued income taxes		150
Total current liabilities	3,708	3,677
Long-term debt		3,368
Other liabilities		1,030
Total liabilities and equity	18,216	17,793
Consolidated Statement of Cash Flows
Other current assets	3	8	1
Other assets		13	(141)
Accrued income taxes		33	43
Other liabilities		(196)	8
Net cash provided by operations	1,888	2,119	1,341
Proceeds from debt	1,091	1,386	547
Net cash used for financing activities	$ (906)	(968)	(834)
Scenario, Previously Reported
Consolidated Balance Sheet
Current deferred tax asset		521
Other current assets		199
Total current assets		6,055
Deferred tax assets		876
Other assets		1,200
Total assets		17,840
Accrued income taxes		178
Total current liabilities		3,705
Long-term debt		3,376
Other liabilities		1,041
Total liabilities and equity		17,840
Consolidated Statement of Cash Flows
Other current assets		(32)	(70)
Other assets		25	(75)
Accrued income taxes		43	43
Other liabilities		(185)	13
Net cash provided by operations		2,112	1,341
Proceeds from debt		1,393	547
Net cash used for financing activities		(961)	(834)
New Accounting Pronouncement, Early Adoption, Effect | Restatement Adjustment
Consolidated Balance Sheet
Current deferred tax asset		(521)
Other current assets		0
Total current assets		(521)
Deferred tax assets		482
Other assets		0
Total assets		(39)
Accrued income taxes		(28)
Total current liabilities		(28)
Long-term debt		0
Other liabilities		(11)
Total liabilities and equity		(39)
Consolidated Statement of Cash Flows
Other current assets		39	71
Other assets		(18)	(66)
Accrued income taxes		(10)	0
Other liabilities		(11)	(5)
Net cash provided by operations		0	0
Proceeds from debt		0	0
Net cash used for financing activities		0	$ 0
Accounting Standards Update 2015-03 | Restatement Adjustment
Consolidated Balance Sheet
Current deferred tax asset		0
Other current assets		(1)
Total current assets		(1)
Deferred tax assets		0
Other assets		(7)
Total assets		(8)
Accrued income taxes		0
Total current liabilities		0
Long-term debt		(8)
Other liabilities		0
Total liabilities and equity		(8)
Consolidated Statement of Cash Flows
Other current assets		1
Other assets		6
Accrued income taxes		0
Other liabilities		0
Net cash provided by operations		7
Proceeds from debt		(7)
Net cash used for financing activities		$ (7)