Griffin Dunne’s years-in-the-making documentary portrait of his aunt Joan Didion moves with the spirit of her uncannily lucid writing: the film simultaneously expands and zeroes in, covering a vast stretch of turbulent cultural history with elegance and candor, and grounded in the illuminating presence and words of Didion herself. This is most certainly a film about loss—the loss of a solid American center, the personal losses of a husband and a child—but Didion describes everything she sees and experiences so attentively, so fully, and so bravely that she transforms the very worst of lif...