Benefit Plans and Other Postretirement Benefits, Changes in Level 3 Pension Plan Assets (Details) - Pension Plans - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		$ 3,083,771	$ 3,010,140
Fair value of plan assets at Dec. 31		2,883,780	3,083,771	$ 3,010,140
Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		206,528	200,402	277,638
Net realized gains (losses)		35,177	29,263	19,399
Net unrealized gains (losses)		(49,291)	(20,016)	(15,645)
Purchases, issuances and settlements, net		(10,083)	(3,121)	5,945
Transfers in (out) of Level 3		0	0	(86,935)	[1]
Fair value of plan assets at Dec. 31		182,331	206,528	200,402
Asset-backed securities
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		3,759
Fair value of plan assets at Dec. 31		2,446	3,759
Asset-backed securities | Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		0	0	14,639
Net realized gains (losses)				0
Net unrealized gains (losses)				0
Purchases, issuances and settlements, net				0
Transfers in (out) of Level 3	[1]			(14,639)
Fair value of plan assets at Dec. 31		0	0	0
Mortgage-backed securities
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		11,047
Fair value of plan assets at Dec. 31			11,047
Mortgage-backed securities | Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		0	0	39,904
Net realized gains (losses)				0
Net unrealized gains (losses)				0
Purchases, issuances and settlements, net				0
Transfers in (out) of Level 3	[1]			(39,904)
Fair value of plan assets at Dec. 31			0	0
Private equity investments
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		151,871
Fair value of plan assets at Dec. 31		126,396	151,871
Private equity investments | Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		151,871	152,849	158,498
Net realized gains (losses)		28,094	25,694	22,058
Net unrealized gains (losses)		(40,848)	(17,573)	(24,335)
Purchases, issuances and settlements, net		(12,721)	(9,099)	(3,372)
Transfers in (out) of Level 3		0	0	0	[1]
Fair value of plan assets at Dec. 31		126,396	151,871	152,849
Real estate
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		54,657
Fair value of plan assets at Dec. 31		55,935	54,657
Real estate | Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		54,657	47,553	64,597
Net realized gains (losses)		7,083	3,569	(2,659)
Net unrealized gains (losses)		(8,443)	(2,443)	8,690
Purchases, issuances and settlements, net		2,638	5,978	9,317
Transfers in (out) of Level 3		0	0	(32,392)	[1]
Fair value of plan assets at Dec. 31		$ 55,935	$ 54,657	$ 47,553

[1] Transfers out of Level 3 into Level 2 were principally due to diminished use of unobservable inputs that were previously significant to these fair value measurements and were subsequently sold during 2013.