Common Shareholders' Equity (Issuance of Common Stock and Forward Sale Agreement) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Nov. 30, 2013	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jan. 01, 2016
Class of Stock [Line Items]
Stock sold during the period	4,500,000
Share Price (in dollars per share)	$ 88.03
Forward sale price (in dollars per share)		$ 124.00
Settlement of shares		12,000,000
Proceeds from forward sale agreement		$ 1,500
Antidilutive securities (in shares)		7,900,000	3,500,000	2,600,000
Forward Counterparty [Member]
Class of Stock [Line Items]
Stock sold during the period	6,600,000
Shares delivered				6,600,000
Proceeds from Equity				$ 552
Adjustments for New Accounting Principle, Early Adoption [Member]
Class of Stock [Line Items]
Unrecognized Tax Benefits					$ (18)
Excess tax benefits		$ 30
Forward Contracts [Member]
Class of Stock [Line Items]
Antidilutive securities (in shares)		12,000,000