Consolidated Statement Of Changes In Shareholders' Equity - USD ($) $ in Millions	Share Capital [Member]	Paid In Surplus [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Total
Balance, Beginning of Year at Dec. 31, 2014	$ 2,450.0	$ 1,358.0	$ 5,188.0	$ 689.0	$ 9,685.0
Net Earnings (Loss)			(5,165.0)		(5,165.0)
Dividends on Common Shares			(225.0)		(225.0)
Common Shares Issued	1,098.0				1,098.0
Common Shares Issued under Dividend Reinvestment Plan	73.0				73.0
Other Comprehensive Income (Loss)				701.0	701.0
Balance, End of Year at Dec. 31, 2015	3,621.0	1,358.0	(202.0)	1,390.0	6,167.0
Net Earnings (Loss)			(944.0)		(944.0)
Dividends on Common Shares			(52.0)		(52.0)
Common Shares Issued	1,134.0				1,134.0
Common Shares Issued under Dividend Reinvestment Plan	1.0				0.9
Other Comprehensive Income (Loss)				(180.0)	(180.0)
Balance, End of Year at Dec. 31, 2016	4,756.0	1,358.0	(1,198.0)	1,210.0	6,126.0
Net Earnings (Loss)			827.0		827.0
Dividends on Common Shares			(58.0)		(58.0)
Common Shares Issued under Dividend Reinvestment Plan	1.0				0.6
Other Comprehensive Income (Loss)				(168.0)	(168.0)
Balance, End of Year at Dec. 31, 2017	$ 4,757.0	$ 1,358.0	$ (429.0)	$ 1,042.0	$ 6,728.0