Schedule I - Condensed Financial Information Of Parent (Statement of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	$ 2,123	$ 2,031	$ 1,565
Cash Flows From Investing Activities:
Proceeds from Collection of Notes Receivable	0	20	95
Contributions to Note Receivable	0	(8)	(89)
Other	5	20	11
Net Cash Provided by (Used in) Investing Activities	(2,141)	(1,976)	(1,717)
Cash flows from financing activities:
Dividends on common stock	(416)	(402)	(390)
Short-term debt, net	257	(413)	346
Repayments of Other Long-term Debt	(395)	(120)	(697)
Issuances of Long-term debt	389	1,197	898
Capital issuance costs	(9)	(12)	(11)
Share-based payments	(83)	(12)	(14)
Net cash provided by (used in) financing activities	(265)	232	127
Net change in cash and cash equivalents	(283)	287	(25)
Cash and cash equivalents at beginning of year	292	5	30
Cash and cash equivalents at end of year	9	292	5
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net cash provided by operating activities	483	551	528
Cash Flows From Investing Activities:
Money pool advances, net	(27)	55	279
Intercompany notes receivable, net	(60)	(96)	(134)
Investments in subsidiaries	(123)	(509)	(280)
Return of investments	0	0	215
Proceeds from Collection of Notes Receivable	0	20	95
Contributions to Note Receivable	0	(8)	(89)
Other	2	(24)	(12)
Net Cash Provided by (Used in) Investing Activities	(208)	(562)	74
Cash flows from financing activities:
Dividends on common stock	(416)	(402)	(390)
Short-term debt, net	206	(284)	217
Money pool borrowings, net	19	14	0
Repayments of Other Long-term Debt	0	0	(425)
Issuances of Long-term debt	0	700	0
Capital issuance costs	0	(6)	0
Share-based payments	(83)	(12)	(14)
Net cash provided by (used in) financing activities	(274)	10	(612)
Net change in cash and cash equivalents	1	(1)	(10)
Cash and cash equivalents at beginning of year	0	1	11
Cash and cash equivalents at end of year	1	0	1
Cash dividends received from consolidated subsidiaries	465	575	340
Noncash Investing activity- investment in subsidiaries	$ 0	$ (38)	$ (19)