Debt (Narrative) (Details) (USD $)	12 Months Ended			0 Months Ended	1 Months Ended	0 Months Ended		1 Months Ended	0 Months Ended	1 Months Ended	3 Months Ended	1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Sep. 30, 2013	Mar. 28, 2014	Mar. 27, 2014	Dec. 31, 2012	May 31, 2014	Oct. 31, 2014	Dec. 31, 2014	May 31, 2014	Oct. 31, 2013	Feb. 28, 2013
Debt Instrument [Line Items]
Repayments of long-term debt	$ 331,000,000	$ 260,000,000	$ 259,000,000
Cost for early redemption	137,000,000	24,000,000	0
2.35% Senior Debt Obligations Due 2019 [Member]
Debt Instrument [Line Items]
Debt instrument, amount				300,000,000
Interest rate	2.35%			2.35%							2.35%
Debt instrument, term				5 years
Senior Debt Obligations Due 2018 [Member]
Debt Instrument [Line Items]
Debt instrument, amount					250,000,000
Interest rate	2.55%				2.55%						2.55%
Debt instrument, term					5 years
Other Debt Facilities [Member]
Debt Instrument [Line Items]
Revolving credit facility, amount outstanding	600,000	1,000,000									600,000
Debt instrument, unused borrowing capacity	260,000,000	282,000,000									260,000,000
Senior Debt Obligations Due 2021 [Member]
Debt Instrument [Line Items]
Interest rate	4.80%										4.80%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, term						5 years
Line of Credit Facility, Current Borrowing Capacity							1,000,000,000
Revolving credit facility, borrowing capacity						1,000,000,000.0
Revolving credit facility, amount outstanding	0										0
Amended Revolving Credit Facility March 28, 2014 [Member]
Debt Instrument [Line Items]
Debt instrument, term							5 years
Revolving credit facility, borrowing capacity							1,200,000,000.0
Revolving credit facility, amount outstanding	0										0
Senior Debt Obligations Due 2015 [Member]
Debt Instrument [Line Items]
Interest rate	5.75%				5.75%						5.75%
Senior Debt Obligations Due 2014 [Member]
Debt Instrument [Line Items]
Interest rate	5.375%								5.375%		5.375%	5.375%
Senior Debt Obligations Due 2017 [Member]
Debt Instrument [Line Items]
Interest rate	2.30%										2.30%
Three-Year Delayed Draw Term Loan Facility [Member]
Debt Instrument [Line Items]
Debt instrument, term								3 years
Revolving credit facility, borrowing capacity			50,000,000					50,000,000
Revolving credit facility, amount outstanding	50,000,000										50,000,000
Interest rate on credit facility	1.17%										1.17%
Senior Debt Obligations Due 2023 [Member]
Debt Instrument [Line Items]
Debt instrument, amount					250,000,000
Interest rate	4.05%				4.05%						4.05%
Debt instrument, term					10 years
3.50% Senior Debt Obligations Due 2025 [Member]
Debt Instrument [Line Items]
Debt instrument, amount				500,000,000
Interest rate	3.50%			3.50%							3.50%
Debt instrument, term				10 years 6 months
Senior Debt Obligations Due 2024 [Member] [Domain]
Debt Instrument [Line Items]
Debt instrument, amount									600,000,000			600,000,000
Interest rate	3.50%								3.50%		3.50%	3.50%
Debt instrument, term									10 years
Senior Debt Obligations Due 2019 [Member]
Debt Instrument [Line Items]
Interest rate										9.25%
Partial redemption of notes										400,000,000
Senior Debt Obligations Due 2015 and Senior Debt Obligations Due 2019 [Member]
Debt Instrument [Line Items]
Partial redemption of notes										630,000,000
Repayments of long-term debt										765,000,000
Cost for early redemption											137,000,000
Senior Debt Obligations Due 2014 [Member]
Debt Instrument [Line Items]
Repayments of long-term debt												320,000,000
Senior Debt Obligations Due 2015 [Member]
Debt Instrument [Line Items]
Interest rate										5.75%
Partial redemption of notes					250,000,000					230,000,000
Repayments of long-term debt													275,000,000
Cost for early redemption													24,000,000
Senior Debt Obligations Due 2013 [Member]
Debt Instrument [Line Items]
Interest rate														4.85%
Revised Purchase Price Allocation For Principal Amount Outstanding of Notes														$ 250,000,000