Debt And Shareholders' Equity (Narrative) (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions

3 Months Ended

12 Months Ended

Mar. 31, 2018

Mar. 31, 2017

Jun. 30, 2018

Dec. 31, 2017

Dec. 31, 2016

Debt And Shareholders' Equity [Line Items]

Schedule of Long-term Debt Instruments [Table Text Block]

Long-term debt is summarized as follows:

(In millions)	March 31, 2018		December 31, 2017
Subordinated notes	$	247	$	247
Senior notes	135		135
Capital lease obligations	1		1
Total	$	383	$	383

Subordinated Debt

$ 247

$ 247

Other Comprehensive Income (Loss), before Reclassifications, Net of Tax

(128)

$ 12

Stockholders' Equity [Abstract]

Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax

0

$ 1

Senior Notes

135

135

Capital Lease Obligations

1

1

Long-term Debt, Gross

$ 383

383

Stock Repurchased During Period, Shares

2.0

1.1

Stock Repurchased and Retired During Period, Value

$ 115

$ 45

$ 345

Treasury Stock Acquired, Average Cost Per Share

$ 53.46

$ 42.43

$ 49.28

Stock Repurchase Program, Authorized Amount

$ 120

Net Shares Issued From Stock Warrant Exercises

1.0

Warrants Sold

3.2

Class of Warrant or Right, Outstanding

2.6

Warrant Exercise Price

$ 36.27

Accumulated Other Comprehensive Income (Loss), Net of Tax

$ (267)

$ (111)

$ (139)

$ (122)

Repayments of Long-term Debt

$ 0

153

Warrant [Member]

Stockholders' Equity [Abstract]

Class of Warrant or Right, Outstanding

29.3

Warrant Exercise Price

$ 35.37

Senior Notes [Member]

Stockholders' Equity [Abstract]

Repayments of Long-term Debt

$ 153