Schedule I - Condensed Financial Information of Parent (Statement of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	$ 2,134	$ 1,791	$ 2,715
Investing Activities:
Decrease in restricted cash	(159)	419	44
(Purchase) sale of short term investments, net	(17)	(728)	(7)
Net cash used in investing activities	(2,366)	(656)	(1,774)
Financing Activities:
Borrowings (payments) under the revolver, net	959	836	1,139
Purchase of treasury stock	(482)	(308)	(322)
Common stock dividends paid	(276)	(144)	(119)
Payments for deferred financing costs	(90)	(158)	(176)
Proceeds from (Payments for) Other Financing Activities	(7)	27	14
Net cash provided by (used in) financing activities	28	(1,262)	(1,136)
Effect of exchange rate changes on cash	(52)	(51)	(59)
Total decrease in cash and cash equivalents	(277)	(103)	(258)
Cash and cash equivalents, beginning	1,539	1,642	1,900
Cash and cash equivalents, ending	1,262	1,539	1,642
SUPPLEMENTAL DISCLOSURES:
Cash payments for interest, net of amounts capitalized	1,265	1,351	1,398
Cash payments for income taxes, net of refunds	388	480	570
Parent Company
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	475	449	418
Investing Activities:
Expenses related to asset sales	0	(4)	(5)
Investment in and net advances to subsidiaries	(221)	(69)	201
Return of capital	501	740	230
Decrease in restricted cash	49	96	50
Additions to property, plant and equipment	(11)	(31)	(11)
(Purchase) sale of short term investments, net	0	(1)	1
Net cash used in investing activities	318	731	466
Financing Activities:
Borrowings (payments) under the revolver, net	0	0	0
Borrowings of notes payable and other coupon bearing securities	575	1,525	750
Repayments of notes payable and other coupon bearing securities	(915)	(2,117)	(1,210)
Loans (to) from subsidiaries	0	263	(152)
Purchase of treasury stock	(482)	(308)	(322)
Proceeds from issuance of common stock	4	1	13
Common stock dividends paid	(276)	(144)	(119)
Payments for deferred financing costs	(6)	(20)	(17)
Proceeds from (Payments for) Other Financing Activities	(18)	0	0
Net cash provided by (used in) financing activities	(1,118)	(800)	(1,057)
Effect of exchange rate changes on cash	0	0	(1)
Total decrease in cash and cash equivalents	(325)	380	(174)
Cash and cash equivalents, beginning	511	131	305
Cash and cash equivalents, ending	186	511	131
SUPPLEMENTAL DISCLOSURES:
Cash payments for interest, net of amounts capitalized	314	373	442
Cash payments for income taxes, net of refunds	$ 0	$ (2)	$ 11