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Shareholder Report, Line Graph (Details) - USD ($)
 12 Months Ended 60 Months Ended 102 Months Ended 120 Months Ended
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Jun. 30, 2016
Dec. 31, 2015
Dec. 31, 2014
C000015147 [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class A Shares at maximum sales charge (Offering Price)                            
Account Value $ 15,039 $ 15,039 $ 15,039 $ 15,039 $ 14,218 $ 12,784 $ 17,016 $ 12,070 $ 12,892 $ 10,293 $ 10,924 $ 10,370   $ 9,729 $ 9,426
Average Annual Return, Percent (0.32%) 1.92%   4.17%                      
C000015147 [Member] | Without Sales Load [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class A Shares at NAV (excluding maximum sales charge)                            
Account Value $ 15,956 $ 15,956 15,956 $ 15,956 15,084 13,563 18,053 12,806 13,677 10,921 11,590 11,002   10,322 10,000
Average Annual Return, Percent 5.78% 3.13%   4.78%                      
C000015149 [Member] | Without Sales Load [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class C Shares at NAV (excluding maximum sales charge)                            
Account Value $ 15,022 $ 15,022 15,022 $ 15,022 14,201 12,769 17,128 12,248 13,174 10,600 11,333 10,836   10,245 10,000
Average Annual Return, Percent 4.97% 2.36%   4.15%                      
C000126484 [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class R6 Shares at NAV                            
Account Value $ 16,607 $ 16,607 16,607 $ 16,607 15,636 14,004 18,570 13,126 13,956 11,099 11,731 11,090   10,360 10,000
Average Annual Return, Percent 6.20% 3.54%   5.20%                      
C000015151 [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class I Shares at NAV                            
Account Value $ 16,357 $ 16,357 16,357 $ 16,357 15,424 13,831 18,368 12,998 13,846 11,027 11,670 11,051   10,348 10,000
Average Annual Return, Percent 6.05% 3.39%   5.04%                      
C000056118 [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class A Shares at maximum sales charge (Offering Price)                            
Account Value $ 16,822 $ 16,822 16,822 $ 16,822 15,191 13,999 14,937 13,052 13,423 10,383 11,272 9,442   8,775 9,424
Average Annual Return, Percent 4.34% 3.38%   5.34%                      
C000056118 [Member] | Without Sales Load [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class A Shares at NAV (excluding maximum sales charge)                            
Account Value $ 17,851 $ 17,851 17,851 $ 17,851 16,120 14,855 15,850 13,850 14,244 11,019 11,961 10,019   9,311 10,000
Average Annual Return, Percent 10.74% 4.62%   5.97%                      
C000070757 [Member] | Without Sales Load [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class C Shares at NAV (excluding maximum sales charge)                            
Account Value $ 16,799 $ 16,799 16,799 $ 16,799 15,170 13,980 15,039 13,240 13,729 10,695 11,701 9,870   9,250 10,000
Average Annual Return, Percent 9.90% 3.81%   5.32%                      
C000171406 [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class R6 Shares at NAV                            
Account Value $ 17,386 $ 17,386 $ 17,386 $ 17,386 15,651 14,376 15,302 13,325 13,651 10,525 11,385 9,492 $ 10,000    
Average Annual Return, Percent 11.09% 4.96% 6.72%                        
C000056119 [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class I Shares at NAV                            
Account Value $ 18,293 $ 18,293 $ 18,293 $ 18,293 16,490 15,142 16,135 14,057 14,424 11,122 12,046 10,071   9,333 10,000
Average Annual Return, Percent 10.94% 4.87%   6.23%                      
C000104365 [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class A Shares at maximum sales charge (Offering Price)                            
Account Value $ 14,030 $ 14,030 14,030 $ 14,030 13,133 12,146 13,803 12,368 12,844 10,494 11,209 10,001   9,125 9,425
Average Annual Return, Percent 0.68% 0.58%   3.44%                      
C000104365 [Member] | Without Sales Load [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class A Shares at NAV (excluding maximum sales charge)                            
Account Value $ 14,886 $ 14,886 14,886 $ 14,886 13,934 12,887 14,645 13,122 13,627 11,134 11,892 10,612   9,682 10,000
Average Annual Return, Percent 6.83% 1.78%   4.06%                      
C000104366 [Member] | Without Sales Load [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class C Shares at NAV (excluding maximum sales charge)                            
Account Value $ 14,019 $ 14,019 14,019 $ 14,019 13,123 12,137 13,893 12,545 13,127 10,804 11,628 10,452   9,612 10,000
Average Annual Return, Percent 5.98% 1.02%   3.44%                      
C000171407 [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class R6 Shares at NAV                            
Account Value $ 14,347 $ 14,347 $ 14,347 $ 14,347 13,393 12,337 13,975 12,479 12,918 10,518 11,199 9,957 10,000    
Average Annual Return, Percent 7.13% 2.12% 4.34%                        
C000104368 [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Class I Shares at NAV                            
Account Value $ 15,257 $ 15,257 $ 15,257 $ 15,257 14,249 13,147 14,901 13,319 13,798 11,247 11,982 10,665   9,711 10,000
Average Annual Return, Percent 7.07% 2.03%   4.31%                      
Standard & Poor's 500 Index [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name S&P 500® Index                            
Account Value $ 34,254 $ 34,254 34,254 $ 34,254 27,399 21,696 26,494 20,585 17,386 13,223 13,829 11,351   10,138 10,000
Average Annual Return, Percent 25.02% 14.53%   13.10%                      
MSCI ACWI Index Net [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name MSCI ACWI Index (Net)                            
Account Value $ 24,183 $ 24,183 $ 24,183 $ 24,183 20,584 16,844 20,633 17,406 14,973 11,827 13,056 10,531 10,000 9,764 10,000
Average Annual Return, Percent 17.49% 10.06% 11.10% 9.23%                      
MSCI ACWI C000171406 Index Net [Member]                              
Account Value [Line Items]                              
Account Value $ 24,468 $ 24,468 $ 24,468 $ 24,468 20,826 17,042 20,876 17,611 15,149 11,966 13,210 10,655      
MSCI ACWI C000171407 Index Net [Member]                              
Account Value [Line Items]                              
Account Value 24,468 24,468 24,468 24,468 20,826 17,042 20,876 17,611 15,149 11,966 13,210 10,655 10,000    
MSCI ACWI C000015147 Index Net [Member]                              
Account Value [Line Items]                              
Account Value $ 34,254 34,254 34,254 34,254 27,399 21,696 26,494 20,585 17,386 13,223 13,829 11,351   10,138  
S And P Global Infrastructure Index Net [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name S&P Global Infrastructure Index (Net)                            
Account Value $ 16,292 $ 16,292 $ 16,292 $ 16,292 14,285 13,504 13,639 12,283 13,136 10,446 11,655 9,788 10,000 8,783 10,000
Average Annual Return, Percent 14.05% 4.40% 5.94% 5.00%                      
Lipper Global Infrastructure Funds Classification Average [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Lipper Global Infrastructure Funds Classification Average                            
Average Annual Return, Percent 7.86% 3.96% 5.78% 5.12%                      
Bloomberg U S Corporate High Yield Bond Index [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Bloomberg U.S. Corporate High Yield Bond Index                            
Account Value $ 16,552 $ 16,552 $ 16,552 $ 16,552 15,299 13,486 15,185 14,423 13,466 11,779 12,029 11,190   9,553 10,000
Average Annual Return, Percent 8.19% 4.21% 5.59% 5.17%                      
Real Asset Income Blended Benchmark [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Real Asset Income Blended Benchmark                            
Account Value $ 15,169 $ 15,169 $ 15,169 $ 15,169 14,061 12,612 14,701 13,214 13,228 11,022 11,797 10,417   9,624 10,000
Average Annual Return, Percent 7.88% 2.78% 4.43% 4.25%                      
Lipper Real Return Funds Classification Average [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Lipper Real Return Funds Classification Average                            
Average Annual Return, Percent 3.84% 4.54% 4.26% 3.45%                      
MSCI US REIT Index [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name MSCI US REIT Index                            
Account Value $ 17,345 $ 17,345 $ 17,345 $ 17,345 15,949 14,022 18,575 12,984 14,048 11,164 11,698 11,134   10,252 10,000
Average Annual Return, Percent 8.75% 4.31%   5.66%                      
Real Estate Securities Blended Benchmark [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Real Estate Securities Blended Benchmark                            
Account Value $ 16,799 $ 16,799 16,799 $ 16,799 15,716 13,964 18,557 12,984 14,048 11,164 11,698 11,134   10,252 $ 10,000
Average Annual Return, Percent 6.89% 3.64%   5.32%                      
Lipper Real Estate Funds Classification Average [Member]                              
Account Value [Line Items]                              
Line Graph and Table Measure Name Lipper Real Estate Funds Classification Average                            
Average Annual Return, Percent 6.41% 3.42%   5.02%                      
S And P Global Infrastructure C000171406 Index Net [Member]                              
Account Value [Line Items]                              
Account Value $ 16,339 $ 16,339 16,339 $ 16,339 14,326 13,543 13,678 12,318 13,173 10,476 11,688 9,816      
Bloomberg U S Corporate High Yield Bond C000171407 Index [Member]                              
Account Value [Line Items]                              
Account Value 15,887 15,887 15,887 15,887 14,684 12,944 14,575 13,844 12,925 11,306 11,546 10,740 10,000    
Real Asset Income Blended Benchmark C000171407 [Member]                              
Account Value [Line Items]                              
Account Value 14,461 14,461 14,461 14,461 13,405 12,023 14,014 12,597 12,610 10,508 11,246 9,931 $ 10,000    
Bloomberg U S Corporate High Yield Bond C000015147 Index [Member]                              
Account Value [Line Items]                              
Account Value 17,345 17,345 17,345 17,345 15,949 14,022 18,575 12,984 14,048 11,164 11,698 11,134   10,252  
Real Asset Income Blended Benchmark C000015147 [Member]                              
Account Value [Line Items]                              
Account Value $ 16,799 $ 16,799 $ 16,799 $ 16,799 $ 15,716 $ 13,964 $ 18,557 $ 12,984 $ 14,048 $ 11,164 $ 11,698 $ 11,134   $ 10,252