Schedule I - Condensed Financial Information Of Parent (Statement of Cash Flows) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net cash provided by operating activities	$ 1,878	$ 1,823	$ 1,967
Cash Flows From Investing Activities:
Other	12	2	2
Net cash used in investing activities	(1,048)	(1,096)	(1,781)
Cash Flows From Financing Activities:
Dividends on common stock	(375)	(368)	(338)
Short-term and credit facility borrowings, net	(581)	(121)	(324)
Issuances:
Long-term debt			1,021
Common stock	65	80	634
Net cash provided by (used in) financing activities	(1,120)	(804)	344
Net change in cash and equivalents	(290)	(77)	530
Cash and cash equivalents at beginning of year	545	622	92
Cash and cash equivalents at end of year	255	545	622
Parent Company [Member]
Net cash provided by operating activities	804	241	270
Cash Flows From Investing Activities:
Money pool advances, net	(276)	18	300
Intercompany notes receivable, net	358	242	(712)
Investments in subsidiaries	(94)	(13)	(831)
Other	(2)	1
Net cash used in investing activities	(14)	248	(1,243)
Cash Flows From Financing Activities:
Dividends on common stock	(375)	(368)	(338)
Short-term and credit facility borrowings, net	(481)	(221)	275
Issuances:
Long-term debt			423
Common stock	65	80	634
Other			(19)
Net cash provided by (used in) financing activities	(791)	(509)	975
Net change in cash and equivalents	(1)	(20)	2
Cash and cash equivalents at beginning of year	4	24	22
Cash and cash equivalents at end of year	3	4	24
Cash dividends received from consolidated subsidiaries	$ 730	$ 368	$ 338