Comprehensive Income - AOCI (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period		$ 11,358,354	$ 13,727,537	$ 13,386,589	$ 13,512,529
Balance, as adjusted						$ 13,236,376	$ 13,515,989
Net current period other comprehensive income		41,826	161,643	405,237	235,792
Balance, end of period		11,270,789	13,870,723	11,270,789	13,870,723
Total
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period		362,339	(148,135)	(1,072)	(186,848)
Cumulative effect adjustment related to ASU adoptions	[1]						(35,436)
Balance, as adjusted						$ (1,072)	(222,284)
Other comprehensive income (loss) before reclassifications				446,333	233,189
Amounts reclassified from accumulated other comprehensive (loss) income				(41,096)	2,603
Net current period other comprehensive income		41,826	161,643	405,237	235,792
Balance, end of period		404,165	13,508	404,165	13,508
Unrealized Gains (Losses) on Debt Securities Available for Sale and Transferred to Held to Maturity
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period				(40,080)	(158,433)
Cumulative effect adjustment related to ASU adoptions	[1]						(25,844)
Balance, as adjusted							(184,277)
Other comprehensive income (loss) before reclassifications				131,414	137,404
Amounts reclassified from accumulated other comprehensive (loss) income				(13,940)	(3,152)
Net current period other comprehensive income				117,474	134,252
Balance, end of period		77,394	(50,025)	77,394	(50,025)
Accumulated Gains (Losses) on Cash Flow Hedging Instruments
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period				91,445	6,175
Cumulative effect adjustment related to ASU adoptions	[1]						(1,040)
Balance, as adjusted							5,135
Other comprehensive income (loss) before reclassifications				314,919	95,867
Amounts reclassified from accumulated other comprehensive (loss) income				(29,149)	2,136
Net current period other comprehensive income		10,933	73,950	285,770	98,003
Balance, end of period		377,215	103,138	377,215	103,138
Defined Benefit Plan Adjustment
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period				(46,666)	(29,495)
Cumulative effect adjustment related to ASU adoptions	[1]						(7,351)
Balance, as adjusted							(36,846)
Other comprehensive income (loss) before reclassifications				0	0
Amounts reclassified from accumulated other comprehensive (loss) income				1,754	3,119
Net current period other comprehensive income				1,754	3,119
Balance, end of period		(44,912)	(33,727)	(44,912)	(33,727)
Unamortized Impairment Losses on Debt Securities Held to Maturity
Accumulated Comprehensive Income [Roll Forward]
Balance, beginning of period				(5,771)	(5,095)
Cumulative effect adjustment related to ASU adoptions	[1]						(1,201)
Balance, as adjusted							$ (6,296)
Other comprehensive income (loss) before reclassifications				0	(82)
Amounts reclassified from accumulated other comprehensive (loss) income				239	500
Net current period other comprehensive income				239	418
Balance, end of period		$ (5,532)	$ (5,878)	$ (5,532)	$ (5,878)

[1] Related to the Company's adoption of ASU 2017-12 and ASU 2018-02 on January 1, 2019.