Schedule I - Condensed Parent Company Financial Statements (Condensed Statements Of Cash Flows) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions
Net income	$ 1,782	$ 1,714	$ 1,323
Net cash provided by operating activities	5,244	3,672	4,511
Net Cash Provided by (Used in) Investing Activities
Purchases of available-for-sale securities	(4,719)	(3,194)	(2,166)
Proceeds from sales and maturities of available-for-sale securities	4,537	3,063	2,261
Other	74	21	6
Net cash used in investing activities	(6,197)	(4,434)	(4,423)
Net Cash Provided by (Used in) Financing Activities
Proceeds from the issuance of long-term debt	4,170	2,570	2,738
Proceeds from the issuance of common stock related to employee benefit plans	23	67	302
Payments for the redemption of long-term debt	(2,498)	(278)	(1,647)
Notes payable and commercial paper	278	208	(55)
Dividends paid	(1,752)	(1,329)	1,284
Other	(5)	(10)	(4)
Net Cash Provided by (Used in) Financing Activities	267	1,202	40
Net increase (decrease) in cash and cash equivalents	(686)	440	128
Cash and cash equivalents at beginning of period	2,110	1,670	1,542
Cash and cash equivalents at end of period	1,424	2,110	1,670
Parent Company [Member]
Condensed Financial Statements, Captions
Net income	1,768	1,706	1,320
Net cash provided by operating activities	(136)	(287)	178
Net Cash Provided by (Used in) Investing Activities
Purchases of available-for-sale securities	(40)	(45)	0
Proceeds from sales and maturities of available-for-sale securities	82	105	36
Distributions from wholly-owned subsidiaries	450	299	350
Notes receivable from affiliates, net	(982)	264	263
Other	8	14	6
Net cash used in investing activities	(482)	637	655
Net Cash Provided by (Used in) Financing Activities
Proceeds from the issuance of long-term debt	1,226	996	522
Proceeds from the issuance of common stock related to employee benefit plans	23	67	302
Payments for the redemption of long-term debt	(75)	0	(274)
Notes payable and commercial paper	584	151	(2)
Notes payable to affiliated companies	0	105	0
Dividends paid	(1,752)	(1,329)	(1,284)
Other	34	17	26
Net Cash Provided by (Used in) Financing Activities	40	7	(710)
Net increase (decrease) in cash and cash equivalents	(578)	357	123
Cash and cash equivalents at beginning of period	845	488	365
Cash and cash equivalents at end of period	$ 267	$ 845	$ 488