Basic and diluted net earnings per common share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income for the period	$ 198	$ 197	$ 411	$ 435
Undistributed Earnings Applicable to Nonvested Shares	1	1	2	3
Dividends	63	57	127	104
Undistributed Earnings, Basic	135	140	284	331
Undistributed Earnings (Loss) Available to Common Shareholders, Diluted	134	139	282	328
Distributed Earnings	54	47	110	86
Net Income (Loss) Available to Common Stockholders, Diluted	$ 188	$ 186	$ 392	$ 414
Weighted Average Number of Shares Outstanding, Basic	179,156	195,583	181,946	196,149
Earnings Per Share, Basic	$ 1.05	$ 0.95	$ 2.15	$ 2.11
Dilutive Effect of Common Stock Warrants	9,318	12,640	9,587	12,627
Dilutive Effect of Stock Options	624	1,024	673	1,083
Weighted Average Number of Shares Outstanding, Diluted	189,098	209,247	192,206	209,859
Earnings Per Share, Diluted	$ 0.99	$ 0.89	$ 2.04	$ 1.97

The total amount of dividends declared in the period for each class of stock and the contractual amount of dividends (or interest on participating income bonds) that must be paid for the period (for example, unpaid cumulative dividends). Dividends declared in the current period do not include dividends declared in respect of prior-period unpaid cumulative dividends. Preferred dividends that are cumulative only if earned are deducted only to the extent that they are earned.

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