Mortgage Banking Activities Mortgage Banking Activities, Loans Serviced for Others (Details) $ in Thousands	Mar. 31, 2018 USD ($)
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	$ 21,586,739
30 to 59 Days Past Due	294,521
60 to 89 Days Past Due	63,349
90 Days or More Past Due	64,211
Total	22,008,820
FHLMC [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	7,976,244
30 to 59 Days Past Due	66,368
60 to 89 Days Past Due	11,988
90 Days or More Past Due	26,817
Total	8,081,417
FNMA [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	6,564,941
30 to 59 Days Past Due	61,463
60 to 89 Days Past Due	9,918
90 Days or More Past Due	23,897
Total	6,660,219
GNMA [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	6,600,444
30 to 59 Days Past Due	162,994
60 to 89 Days Past Due	40,317
90 Days or More Past Due	11,888
Total	6,815,643
Other [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	445,110
30 to 59 Days Past Due	3,696
60 to 89 Days Past Due	1,126
90 Days or More Past Due	1,609
Total	$ 451,541