Debt And Lines Of Credit Debt and Lines of Credit (Debt Extinguishment Footnotes) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount	[1]		$ 993	$ 266	$ 2,151
Debt Instrument, Maturity Date Range, Start			Apr. 01, 2015	Apr. 01, 2015	Apr. 01, 2015
Debt Instrument, Maturity Date Range, End			Dec. 01, 2030	Dec. 01, 2030	Dec. 01, 2030
Variable Interest Entity, Primary Beneficiary [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount					$ 630
Minimum [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			1.57%	1.57%	1.57%
Maximum [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			9.38%	9.38%	9.38%

[1] Reductions related to notes with interest rates ranging from 1.57% to 9.38% with original maturities from 2015 to 2030 for the years ended December 31, 2017, 2016 and 2015. Includes the $630 million payment for a portion of the Special Purpose Entity Liability for the year ended December 31, 2015 (see Note 12 Variable Interest Entities).