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 Financial Statements, Captions [Line Items]
Net cash provided by operating activities	$ 2,017	$ 1,551	$ 1,693
Cash Flows From Investing Activities:
Proceeds from Collection of Notes Receivable	20	95	6
Contributions to Note Receivable	(8)	(89)	(5)
Other	20	11	1
Net Cash Provided by (Used in) Investing Activities	(1,976)	(1,717)	(1,723)
Cash flows from financing activities:
Dividends on common stock	(402)	(390)	(388)
Short-term debt, net	(413)	346	368
Repayments of Other Long-term Debt	(120)	(697)	(399)
Issuances of Long-term debt	1,197	898	278
Capital issuance costs	(12)	(11)	(2)
Other	2	1	0
Net cash provided by (used in) financing activities	246	141	(149)
Net change in cash and cash equivalents	287	(25)	(179)
Cash and cash equivalents at beginning of year	5	30	209
Cash and cash equivalents at end of year	292	5	30
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	537	514	453
Cash Flows From Investing Activities:
Money pool advances, net	55	279	(371)
Intercompany notes receivable, net	(96)	(134)	(23)
Investments in subsidiaries	(509)	(280)	(50)
Return of investments	0	215	1
Proceeds from Collection of Notes Receivable	20	95	6
Contributions to Note Receivable	(8)	(89)	(5)
Other	(24)	(12)	(3)
Net Cash Provided by (Used in) Investing Activities	(562)	74	(445)
Cash flows from financing activities:
Dividends on common stock	(402)	(390)	(388)
Short-term debt, net	(284)	217	368
Money pool borrowings, net	14	0	0
Repayments of Other Long-term Debt	0	(425)	0
Issuances of Long-term debt	700	0	0
Capital issuance costs	(6)	0	0
Other	2	0	0
Net cash provided by (used in) financing activities	24	(598)	(20)
Net change in cash and cash equivalents	(1)	(10)	(12)
Cash and cash equivalents at beginning of year	1	11	23
Cash and cash equivalents at end of year	0	1	11
Cash dividends received from consolidated subsidiaries	575	340	570
Noncash investing activity - divestiture	0	0	494
Noncash Investing activity- investment in subsidiaries	$ (38)	$ (19)	$ 0