Retirement Plans (Amounts Recognized as a Component of AOCI) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Settlement costs recognized during year			$ (44)
Pension Benefits [Member]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Accumulated other comprehensive loss at beginning of year	$ 532	$ 412
Net actuarial gain (loss) recognized during year	(29)	(20)
Net actuarial loss (gain) occurring during year	81	140
Settlement costs recognized during year			(44)
Net amount recognized in comprehensive income for the year	52	120
Accumulated other comprehensive (gain) loss at end of year	584	532	412
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Accumulated other comprehensive loss at beginning of year	119	5
Net actuarial gain (loss) recognized during year	(8)	(3)
Prior service (cost) credit recognized during year	5	4
Net actuarial loss (gain) occurring during year	(136)	113
Net amount recognized in comprehensive income for the year	(139)	114
Accumulated other comprehensive (gain) loss at end of year	$ (20)	$ 119	$ 5